Virtually ever major mechanical component, including the engine, transmission, axles, suspension, steering, brakes, wheels and tires is different on the 2500-series Yukon XL.The SLE 2WD 2500 ($39,585), SLE 4WD 2500 ($45,685) and the SLT 2WD 2500 ($46,895) and 4WD SLT 2500 ($49,740) come only with a 352-hp 6.0-liter V8 with 383 pound-feet of torque, a six-speed automatic, and rear or 4WD.

Also offered are the luxurious 2WD Denali ($52,850) and AWD Denali ($55,935).The Denali's all-wheel-drive system lacks low-range gearing.The Denali models come with a 6.2-liter V8 that produces 403 horsepower and 417 pound-feet of torque, six-speed automatic transmission and GMC's Autoride active electronic suspension.Denali AWD EPA numbers are 12/19 on gasoline and 9/14 on E85.

They all have a tow/haul mode which reduces upshifting and downshifting, and also shifts quicker, so the transmission doesn't work so hard when pulling a big load.Transmission oil temperature is part of the instrumentation (along with a tire-pressure monitor).

The SLE1 standard equipment includes cloth upholstery; dual-zone manual climate control; auxiliary rear AC; AM/FM/CD/MP3/XM six-speaker stereo; Bluetooth; cruise control; OnStar Safe & Sound with one year subscription; driver information center; power windows/locks/heated mirrors with manual folding; leather-wrapped, tilt steering wheel with audio controls;; 40/20/40 split front bench seat; six-way power driver's seat; 60/40 split folding second-row bench seat; 50/50 third-row split folding seat; automatic headlights; roof rails; side steps; locking rear differential; three power outlets; P265/70R17 all-season tires on bright aluminum wheels; tow package (receiver hitch, seven-pin wiring harness); intermittent rear wipe/wash; and floor mats.4WD models also get an aluminum-block engine, 3.42:1 axle ratio, and front tow hooks.

Major options for the SLE1 are a $1060 Convenience package (adjustable pedals, remote start, rear park assist, rearview camera), fog lamps and tow hooks for 2WD ($190), CD changer audio upgrade ($295), integrated trailer brake controller ($200), and towing cooler package ($230).

SLE2 (about $900 above SLE1) adds rear audio controls with headphone jacks (you supply headphones), power front bucket seats and center console, power outlets, fog lamps, tow hooks, and center roof rails.

SLT1 models add to SLE2 three-zone automatic climate control, Bose audio system, auto-dimming inside mirror, rear park assist, remote start, adjustable pedals, and universal remote.At the SLT level you can upgrade to Autoride suspension with rear self-leveling ($1120), the 6-liter engine ($1095) and second-row bucket seats ($590).

SLT2 (roughly $800 above SLT1) adds leather upholstery (vinyl third row), more adjustable front seats, two-person driver memory, heated front and second row seats, and power folding mirrors w/signals and parking tilt-down.Options include virtually anything not standard, including navigation, rear seat entertainment, and moonroof ($4790 as the Sun/Entertainment/Destination package), third row screen ($600), Preferred package (rain-sensing front wipers and power liftgate, $675), 20-inch wheels ($1795-1995), rearview camera in mirror ($450), and power release second-row bench ($425).

Denali models come fully loaded, with a wood and leather-wrapped, heated, power-tilt steering wheel; heated first- and second-row seats; 12-way power front seats with lumbar adjustment; memory for the driver's seat and mirrors; power-folding second-row seats; removable three-passenger split-folding third-row seat; power-folding exterior mirrors with integrated turn signals, driver's side auto-dimming and reverse tilting; rain-sensing wipers with heated washers; power liftgate; roof rack, Autoride suspension with rear load-leveling; Bluetooth; 10-speaker Premium Bose Centerpoint Surround Sound System; 403-hp 6.2-liter engine; added noise insulation and cooling capacity; and 20-inch wheels and tires (18-inch wheels are available for a $995 credit, for poor roads, tire chains, etc.).

Since a Denali has features like an SLT2 and then some, factory options are limited to those in the Sun, Entertainment and Destinations Package ($4,790, or separately), Side Blind Zone Alert ($500), and heated/cooled front seats ($650).The integrated trailer brake controller is not listed among Denali options, and the tow rating is less than a 2WD XL 1500.

Regardless of model options are often interdependent with ifs, ands, or buts.For example, a 6-liter upgrade ($1095) usually requires Autoride suspension ($1120) as well.

Safety equipment on all models includes dual frontal airbags, head-protecting curtain side airbags, four-wheel-disc anti-lock brakes with electronic proportioning, and StabiliTrak, GM's electronic stability control with anti-rollover mitigation and traction control.Options include rear park assist, two rearview camera choices, and on Denali, Side Blind Zone Alert.Side airbags are not available.The XL earned the maximum five stars in the government's head-on crash tests.

The Suburban and Yukon XL are familiar vehicles on the road.They share sheetmetal styling but differ in details like the grille, bumpers and lamps.These are big boxes but quite smooth, rather like an ocean liner's long flat sides and tapered ends.The Denali XL adds some of the bling found on Cadillac's Escalade ESV.

The running board/side steps are integrated and unobtrusive, extending no farther than necessary, with a black grippy coating; powered retractable steps are available on some models.The tinted glass behind the C-pillar is expansive, and adds to both appearance and function.The front end has a clean appearance, with beefy block-like headlamps over a front bumper fascia.Doors close with a reassuring thud.

Wheels change perceptions of the XL, the standard aluminum wheel a nice piece for look and function.For 2009 a chrome-clad 20-inch wheel is available but this merely adds a chrome-plated plastic cover to an existing wheel and could fall off or pack snow and muck depending on how you abuse your truck.Dealers offer a host of dress-up items, including wheels up to 22-inch.

The rear window opens separately, which is convenient for loading lighter bags and cargo.The larger liftgate is aluminum and balanced, upgradeable to power for those accustomed to a push-button world.Roof racks can carry unwieldly items that aren't too heavy, but be sure to load with the hatch open or after the cargo area is filled so the roof load doesn't interfere with the open hatch.

The instrument panel and center stack are elegant and worthy of a higher-end vehicle.The Denali model is richer still, with a wood and leather-wrapped steering wheel, nuance leather darker wood trim than the other models.On all models the steering wheel is net perfectly ahead of the driver, something to consider if you frequent a chiropractor.

We found the touch-screen radio/navigation system easy to use, easier to operate than in many upscale cars, like those German brands with a singular circle logo, for example.We set the radio stations we liked and could quickly switch from favorite XM to AM to FM stations with the push of a single button; many vehicles require switching bands, then switching stations.The system warned of traffic incidents 19 miles ahead in our direction of travel, and has five groups of favorite stations for user assignment.

The switchgear is simple, and the instrumentation is clean.The console is huge, with a deep storage box and a tray on top.The glovebox is large.Two cupholders are provided in a removable tray forward of the console and they work very well.There's another cupholder in each door pocket.A slot in the dash just left of the turn signal is perfect for coins or toll-road tickets.The pedals are adjustable, to accommodate short and tall drivers with the press of a button.

For reversing into tight confines, avoiding backing over a person, pet or play-toy, or easier trailer hitching, two rearview camera systems are offered.One is integral with the navigation system and the image appears on the nav screen; the other shows the image on the inside-rearview mirror, so you get side-by-side near and far views to the rear.

The Yukon XL can seat six, seven, eight or nine passengers, depending on the seats selected.Our SLT had the second-row bucket seats, with room for seven, in a two/two/three configuration.

The second row offers good room, nearly matching the front.Second-row passengers in bucket seats have their own console, with an elbow tray, o cupholders each, audio controls and if equipped, the DVD screen overhead; the bench-seat second-row may be ordered with power releases to fold.With the touch of a button on the instrument panel or C-pillar, the seatbacks fold flat against the lower cushions, and then the seats flip up against the backs of the front seats.

The third row 50/50 seat has three seatbelts and two headrests.If you want to carry long items down one side the rear row becomes a one person seat; most vehicles with a third-row seat split it 60/40 so you can carry six people plus long pieces.The third-row seats fold easily but not flat into the floor like most of the competition; for a longer flat cargo floor the third row must be taken out (and these aren't light baby seats) and left behind.

Head room in the third row is good, and leg room is okay (34.9 inches); the Expedition EL and Navigator L have a distinct advantage here because of their independent rear suspension.There is a great view through the wraparound glass, so it doesn't feel cramped or claustrophobic back there.Third-row climate control vents are inconveniently located in the headliner over the heads of the second-row passengers, but they can be aimed rearward toward the third-row passengers' knees.The second-row passengers have their own vents in the headliner, too, over their laps.

Cargo space is where the Yukon XL excels.There's 137.4 cubic feet of storage behind the front seats, with the second row folded and third row removed.Even with all seats in place, there's still 45.8 cubic feet of cargo space behind the third row.However, it's a nuisance to remove the third row for optimal storage space.

The lift-over height at the rear bumper is relatively high, about the same as a pickup, so it's not easy to climb up into the cargo compartment to reach things, especially since there are no grab handles.

GM's trusty 5.3-liter Vortec V8 is the standard choice and it's a good one, making 310 horsepower and 335 pound-feet of torque; smooth and not too raucous, though not as torquey as the Expedition's 5.4 or Sequoia's new 5.7-liter V8 are also quite impressive.

And for 2009 all Yukon XL's compete on a level playing field with Expedition, Navigator and so on because a six-speed automatic transmission is standard across the range.Fifty percent more gears offers better fuel economy or better performance, usually both since peak performance is infrequently called for.The differences will be more pronounced when towing, and we would choose the no-charge 3.42:1 axle ratio if we planned on anything more than lightly-loaded flat-terrain highway cruising.

If you need more power for towing with your 1500, the optional 366-hp 6.0-liter V8 boasts 376 pound-feet of torque, and the extra power comes with only a nominal dent in fuel economy.

If you have a trailer of 6500-7000 pounds or more and plan on towing with the Suburban full of gear and people, best to consider the 2500 XL.It has a heavy-duty 6-liter V8 with a bit less horsepower but more torque, stronger axles and transmission, stouter steering, suspension and brake systems and truck-service wheels and tires.It is for all intents and purposes a ¾-ton pickup with a nine-seat body on top.Also noteworthy to travelers, the 2500-series has a much larger fuel tank (39 gallons versus 31.5) so its effective range is superior to the 1500.

You can also opt for the Denali XL, with its Corvette-related 6.2-liter engine making 403 hp and 417 pound-feet of stump-pulling twist.Denali tow ratings are the lowest in the XL line and there is no 4WD version for off-road use; it's more likely employed as a six-seat fashion accessory or alpine limousine.

Active Fuel Management is standard on the 5.3-liter V8 and the 6.0-liter V8 in 1500 models.AFM shuts down four of the eight cylinders when they're not needed to save fuel.But at this size and weight all the cylinders are needed most of the time so the fuel saved is limited.A Yukon/Tahoe Hybrid, or BMW X5 or Mercedes GL320 diesel are the only three-row SUVs with decent fuel economy, and there is no Hybrid Yukon XL.

Ride quality in the Yukon XL is excellent, overall.Even when the optional 20-inch wheels are chosen, the suspension deals deftly with road imperfections and potholes but you feel them more.We prefer taller tires on our trucks, however.The Yukon XL is very stable, though it wallows a bit on undulating freeways.Autoride, the optional rear self-leveling and active suspension, electronically adjusts to the road as read by sensors.It reduces body lean in corners, rough road busy-ness and nose-dive under hard braking.

The 1500's rack-and-pinion steering feels fairly direct, though as in other big SUVs it is a bit slow; the 2500 series steers like a new pickup, a bit heavier but confidence inspiring.Also like all large SUVs, the Yukon XL is prone to body lean in turns and doesn't respond well to quick changes of direction.It's a full-size truck (think three tons, higher center of gravity) and needs to be driven accordingly and with respect for others, not like it's a sports car.

Hard crosswinds can blow it around.Driving in an 25-mph crosswind on the freeway at 75 miles per hour, our Yukon XL swayed all over the road, because of its billboard-like profile.Tires, and whether or not you have Autoride or a 2500, will both alter this behavior, and it isn't unique to the Yukon XL among big boxes.

The brakes are all vented discs with antilock, and perhaps the biggest improvement in this generation Yukon.New for 2009 is an integrated trailer brake controller that gives excellent control and eliminates any installation hassles; we would spend the $200 even if we didn't currently own a trailer.

The Yukon XL is a great choice for a big family towing cars, boats, horses, and travel trailers.Maximum towing capacity is 8100 pounds on 1500 and 9600 pounds on the 2500; subtract 1500-2500 pounds if the Yukon is fully loaded.With its long wheelbase and heavy-duty construction, the Yukon XL is a stable platform for towing while offering the interior cargo advantages of a full-size SUV.The standard 5.3-liter V8 can be upgraded to a 6.0-liter V8, the only size offered on 2500-series, and Denali uses a 403-hp 6.2-liter V8.

The Yukon XL seats six to nine people, depending on configuration.There are many vehicles that seat seven people without taking up so much space to do it, but few with so much room left over for cargo.

The optional leather seats are comfortable while the third row is vinyl in deference to (probably sloppy) riders.The driver sits way up high and feels like he or she is master or mistress of his or her domain.The pedals adjust for long or short legs.The instruments and gauges are best-in-class, elegantly clean yet very functional.Interior small items storage is intelligently designed and all over, including a huge center console.

Those in the second row will find a lot of leg room.Heated bucket seats with a center console between them are available for the second row, turning them into first-class accommodations; and there is an optional power folding option, making it easier for third-row passengers to climb in.There's even decent legroom and good headroom in the third row.

At the top of the line is the Yukon XL Denali.The Denali is almost a separate breed.It has its own engine, a 6.2-liter V8 rated at 403 horsepower and 417 pound-feet of torque.The Denali is offered with 2WD or all-wheel-drive for inclement weather but not serious off-road use.The Denali comes standard with the AutoRide active electronic suspension, which is optional on the regular Yukon XL.

A liftgate is available that raises and lowers under power, a Bose sound system, a navigation system, and a DVD rear-seat entertainment system are available.Rearview cameras are standard with navigation and available for others with display in inside mirror.

For 2009 all Yukon XL's get a six-speed automatic transmission, OnStar 8.0, Bluetooth, and available features such as an integrated trailer brake controller, XM radio NavTraffic, and Side Blind Zone Alert.Denali adds a power adjustable steering column and available heated/cooled front seats.The Yukon XL was completely redesigned for 2007.

Yukon XL competes for shoppers with the Chevy Suburban (essentially same equipment and pricing), Ford Expedition EL, and if cargo space isn't as important as tow rating the Toyota Sequoia.Denali XL alternatives include the Lincoln Navigator L, Cadillac Escalade ESV, Mercedes-Benz GL450, and BMW X5 4.8i.

NewCarTestDrive.com correspondent G.R.Whale reported from Los Angeles, with Sam Moses in Portland, Kirk Bell in Chicago.