The GMC Sierra HD pickups were thoroughly redesigned for 2007, so changes for 2008 are limited to smaller items like seat adjusters, gauges, and adding XM Satellite Radio capability.

The GMC Sierra HD offers styling unique to GMC, so it's not just a Chevy Silverado with a different grille.

As with all heavy-duty pickup lines, the Sierra HD offers plenty of configurations with three cab sizes and two bed sizes in 2WD or 4WD.But it also offers two separate interior concepts, something the other guys can't match.And GM offers the only HD pickup with a six-speed automatic as standard (an option only on the Dodge Ram diesel).Its standard 6.0-liter gas V8 is rated higher than anyone else's, as is the 6.6-liter diesel.And only GM includes OnStar as standard.

Almost everything you can get in a GMC sport-utility is available here, including a subwoofer-equipped sound system, navigation, driver memory system, heated leather seats (and heated windshield washer fluid) and a moonroof.At the other end of the spectrum, for the entry price of around $24,000 you get a functional pickup with real load-carrying ability and all the safety bits of the top-line model.

The trick in buying a GMC Sierra HD is to give fair consideration and choose wisely.Compute the permutations among three cabs, two weight classes, two beds, two engine/transmission combinations, two drive systems and four trim levels, and then sort out options that cover everything from a diesel radiator cover to rear park assist, and you can see why prices run from that base $24,000 to well past double it.

GMC nomenclature labels trim levels as commercial-grade Work Truck, popular SLE (1 and 2), and premium SLT that resembles a Yukon sport-utility up front.

Basic WT fare includes a split vinyl bench seat (and split rear seat on four-door cabs), stereo radio with XM satellite, air conditioning, six-speed automatic transmission, tire pressure monitors, and ABS.

Mid-level SLE models include all basic equipment and add cruise control, chromed steel wheels, electronic shift for 4WD, auto-dimming mirror and compass, driver lumbar, locking seat cushion storage, and leather-wrapped steering wheel.The SLE2 package adds fog lamps and interior upgrades such as cloth-upholstered power-adjustable front seats and redundant controls on the steering wheel.

SLT badges are reserved for the priciest Sierras, those with an interior modeled after GMC luxury utilities.These include as standard leather upholstery with 12-way power and heated front seats, two-person driver memory, heated windshield washer fluid system, locking differential, remote start, towing package, 17-inch aluminum wheels, and a Bose audio system with subwoofer.

Base power for all GMC HDs is the latest 6-liter V-8 with an iron block for durability and variable valve timing for efficiency; it rates 353 hp and 375 lb-ft of torque (312 hp for GVWR above 10,000 pounds).The sole option is a 6.6-liter Duramax turbodiesel, at 365 horses and 660 lb-ft of torque.A six-speed automatic is the only transmission offered, and on diesels it adds $1,200 to the engine's roughly $7,200 tab.

Sierras can be set up for anything from a night on the town--moonroof, satellite radio, navigation--to a year on the ranch or fleet garage with snow plow prep, integral trailer brake control, remote start, and power takeoffs.Determining exactly the right model and options will take careful and honest shopping because of the sheer number of choices.

Safety equipment includes frontal airbags, front seat belt pretensioners (a first for HD pickups), ABS, and OnStar.

The wallpaper sized, ruby red GMC logo makes its origin plainly obvious but the bumper that blends into the fenders gives a much cleaner look and is unusual in HD pickups.Increased frame stiffness allows a smaller gap between the cab and body, and combined with the more aerodynamic windshield and narrower door gaps, makes the Sierra much quieter than its predecessor.

The box sides are deeper by an inch-and-a-bit, the tailgate has a optional lock and assist for closing it with less effort, and the cargo management option fits rails to three sides of the bed; these can be used for tie-down points and to carry a variety of tool or utility boxes.The stoutest Sierra HD's can tow 13,000 pounds with the new 2.5-inch receiver hitch, and the new dual-element mirror and trailer brake control options will lower the stress level.

Most HD pickups have external dimensions close to each other and the Sierra is similar; more than six-and-a-half feet wide outside and room for a 4x8-foot sheet of building material to ride flat in the long bed.In 4WD versions the Sierra is slightly lower than competing pickups, and that inch or two could make the difference in commercial garages or fifth-wheel/bed clearance.

The Sierra HD SLT is very low-profile, sleek, and speaks of good fit and finish.All other models use a more conventional pickup layout, with a higher dash section that goes across the middle and leaves the center open for middle riders, manual-shift transfer case, or communications and safety equipment.

Perhaps not as stylish as the SLT's, the standard dash is the more functional of the two and equally well assembled (and gets the same improvements).It offers more options in small storage, a second glove box (with an awkward latch), locking storage area with power point beneath the center seat section, more places to add accessory switches, radio and ventilation controls are up higher near line of sight, and the materials produce less glare in low-lying sun and night construction areas.Adjustable pedals and a tilt wheel are available, though the wheel does not telescope and is offset slightly from the seat centerline.

A regular cab has room for a XXL-sized gent and space behind the seat for his coat and boots.Extended cabs have articulated side doors that swing 170 degrees for easier loading, the windows in those doors roll down flush, and the seat cushion folds up for more storage.Crew cabs are the obvious choice for anyone hauling more than youngsters on a regular basis, just be sure the middle rider knows there is no headrest.Note that the sunroof shade on high-line versions is literally a shade (like that on a Mini) and not a solid cover, and the interior will warm faster on sunny days.

Operating controls are clearly labeled and logically placed, and the shifter offers the typical D and 1 positions, with an M position and thumb tab for individually selecting any intermediate gear.If there's a drawback it is the quantity of similarly-shaped and labeled small buttons that butterfingers may have some issues with.Door switches have been revised so your guard dog won't wind the window up, but he may still lock you out; fortunately, OnStar (and the turn-by-turn navigation it offers) is standard and includes a few months free service.

The fact that the Sierra interior, especially on SLT models, is the most like a car will certainly find favor with those who need a pickup rather than just want one.Apart from turning circle and size, it takes no more to drive this than to drive any other GMC.

With many models over 7,000 pounds empty, the Sierra HD is a lot of mass to move around, and while the new 6-liter has broadly the same horsepower as the old big-block, torque is down roughly 80 lb-ft.Torque is what gets any load moving, up to about 45 mph, and helps keep it moving on grades.However, the six-speed transmission makes up for a lot, so the absence of a big-block is most noticed in low-range 4WD and the less-forceful shove in your back when you leave a traffic light.The 6.0 and six-speed automatic will do about 90 percent of what the 8.1-liter did, and generally use a bit less gas in the process.Remember however, that horsepower on the dual-rear wheel 3500 6.0 is lowered to 312 hp, making an even better argument for the diesel.

With 660 lb-ft of torque available at a much lower engine speed and 365 hp, the Duramax turbodiesel option blows the 6-liter into the weeds for pulling power and fuel economy, though you might say at $8400 for the powertrain it ought to.Much of the added expense from last year is due to the new emissions requirements for diesel engines, reductions of 90 percent in some cases, and the diesel exhaust pipe stays clean and steel-colored inside where the gas engine's is black.The next generation of induction systems has also made the diesel much quieter; your riders may not know it's a diesel if you don't tell them.

Pickups of yore tended to buck like broncos on uneven surfaces like turnpike expansion joints, with the bed trying to bounce one direction and the cab the other.Often a function of wheelbase, this can't be completely eliminated in a long vehicle like a Sierra HD, but it does an admirable job of mitigating the motion.

There's heft to the feel of a Sierra, from the way it takes big bumps to the steering and throttle inputs.Its handling characteristics are benign and amount to basic plowing if you push too hard.All-terrain tires give better grip on dirt roads, at the expense of steering precision and noise on tarmac.

Like all big 2WD pickups the Sierra uses all-vented disc brakes with ABS, and independent front suspension.However, only the GM heavy-duty pickups use the same design on 4WD models, giving them a lower nose and more responsive steering.Again, like any big pickup, the tail is prone to kick over impacts with an empty bed; the Sierra is similar to others although it may feel it has more kick because the front is softer.

The optional integrated trailer brake controller will apply your trailer brakes smoother than any aftermarket controller and works in concert with the Sierra's braking system.This controller, however, is not compatible with all brands of electric-hydraulic disc brakes becoming more common on high-end RVs.

The 2.5-inch receiver hitch allows conventional trailer ratings to 13,000 pounds, higher than many competitive offerings; the maximum for fifth-wheels 16,700 pounds.The strongest Sierra HD will haul 23,500 pounds gross combined: the truck, fuel, passengers, cargo, and trailer.

G.R.Whale filed this report to NewCarTestDrive.com from California.