The Sierra is built on a stiff platform for a smooth ride and sharp handling.The GMC Sierra shares platforms with the Chevy Silverado but its exterior styling is quite different.Sierra interiors offer a choice of two dashboard styles.

The 2008 GMC Sierra is offered in a Denali version, which makes for a comfortable, luxurious, pickup with the emphasis on performance rather than payload and towing capacity.The Sierra Denali offers the same sort of higher-line content as GMC's upscale Yukon Denali sport utility.

Amongst the various cab styles, bed lengths, and eight engine choices (of five sizes) the Sierra offers many permutations.There are limitations however, such as the biggest engine is limited to the Denali, the 6-liter does not go in regular cab or extended cab long bed trucks, and manual transmissions are not offered.

The extended cab has two rows of seats with rear-hinged rear access doors that open 170 degrees and have roll-down windows.The extended cab can be equipped with either a short bed (5-foot, 8-inch), standard or long bed.The extended cab can be equipped with seating for five or six.

The crew cab has two rows of seats and four front-hinged doors, like those on a Yukon.The crew cab can be equipped with seating for five or six and comes with the short bed.

Standard equipment on the Work Truck ($17,070) includes vinyl seating surfaces, air conditioning, AM/FM/XM radio, one-year of OnStar, daytime running lights, tire pressure monitoring system, Smooth Ride suspension, 17-inch wheels, chrome bumpers.

The SLE ($24,690) adds a CD player, cruise control, cloth seats, a rear-window defogger, auto-dimming rearview mirror with compass and outside temperatures, leather-wrapped steering wheel, fog lamps, handling/trailering suspension, carpeting and power door locks/windows/mirrors.To this, SLE2 ($28,465) adds premium cloth seats, dual-zone air conditioning, a floor console, six-way power driver and front passenger seats, audio controls on the steering wheel, and machined aluminum wheels.

The SLT ($30,860) adds leather seat trim, a unique instrument panel, six-disc CD changer with Bose sound system, heated windshield washers, front bucket seats with 12-way power adjustment and heat, and polished aluminum wheels; crew cab models also get a rear-seat audio system.

The Denali ($38,095) includes a top-flight interior with leather, heated and powered front seats, unique woodgrain console, side curtain airbags, dual-zone climate control, park assist and so on.Denali options include a heated steering wheel, sunroof, and rear-seat entertainment.Denali comes only as a crew cab with a 403-hp 6.2-liter V8 engine, six-speed automatic transmission and rear or all-wheel drive.

The All Terrain model, available as a late-2008 model, features the Z71 off-road package, heavy-duty trailer package, 18-inch wheels, Rancho shocks, and myriad cosmetic enhancements.When ordered with SLT trim, exclusive two-tone leather is used.All Terrain is available as an extended cab standard box or crew cab, 2WD or 4WD with 5.3-liter or 6-liter engine.

Options for the Seirra include head curtain airbags, a locking rear differential, StabiliTrak, towing and trailering equipment, and a power sunroof.

Safety features include dual front airbags and a tire-pressure monitoring system.Optional head curtain airbags automatically inflate when sensors sense a severe impact to provide extra protection in the event of a rollover or secondary collision.Also available: driver and front-seat passenger side-impact air bags; anti-lock brakes, StabiliTrak electronic stability control with rollover mitigation technology, Autotrac active transfer case, ultrasonic rear park assist, OnStar emergency notification.

The Denali gets its own chromed grilles, both the upper section and the air vent below the front bumper, and the bumpers are painted to match.

The hood has a pair of long, narrow V-shaped power bulges and leads back to a steeply raked windshield.The windshield is tilted back for improved aerodynamics and enhanced highway fuel economy.

The side view features slightly bulging and elongated fender flares that sweep down behind the headlamps.The sides of the cargo bed are higher than on previous models, and the exterior of the tailgate is sculpted, enhancing the rear view of the truck.Stacked tail lamps are on either side of the tailgate.

Two new reds are available on a truck that looks taller and stronger than its predecessor, yet also has improved aerodynamics.Engine choices include a V6, a 4.8-liter V8, four 5.3-liter V8s (iron and aluminum blocks, some E85 flex-fuel capable, all with Active Fuel Management that disables some cylinders for fuel economy), a 6-liter V8, all with four-speed automatic transmissions, and on the Denali only a 6.2-liter and six-speed auto.Except for Denali, EPA ratings run 13-15 city, 17-20 highway, and on E85 those numbers drop substantially.

An optional cargo management system is available for the bed with side rails and various cargo-carrying and cargo-controlling boxes and dividers and tie-downs.

The GMC Sierra and Chevy Silverado are built on the GMT900 platform that debuted in 2007 and shares many underpinnings with the Yukon SUV.The pickups get a unique rear suspension and frame section that is 245 percent stiffer.The Sierra and Silverado share mechanical components, with the exception of the unique features found on the Sierra Denali.

Compared with the previous-generation, the current frame is 234 percent stiffer in torsional rigidity, 62 percent more resistant to bending and 136 percent stiffer laterally.This yields a smoother ride and better handling.It also allowed the engineers to reduce the gap between the truck bed and passenger compartment as well as the gaps between fenders and bumpers, all of which enhances aerodynamics and fuel efficiency.

The front suspension uses a coil-over-shock setup and the rack-and-pinion steering gear is mounted to the engine cross member frame.The truck also has a new rear axle design with shocks absorbers mounted outboard and more upright for better dynamic control.

The 'pure pickup,' as it's called, has a unique dashboard that is more driver-oriented and has larger switchgear and door handles that are designed to be easily manipulated by those wearing work gloves.The pure pickup interior includes a 40/20/40 split front bench seat with the center section folding down to provide a large storage compartment and wide armrest.

The SUV-style luxury-oriented interior puts audio and ventilation system controls more easily within reach of the front-seat passenger and has two front bucket seats with a fixed center console with assorted storage compartments.

Either dashboard sports full analog instrumentation, and many have more info available through digital display.Operating controls are GM simple, especially on the pure pickup, while the top-line models central dash has many small white-on-black buttons that may require a short learning curve.Some drivers report peculiar ergonomic details as the steering wheel is slightly offset from the seat centerline.

Rear seating is provided for three people in the extended and crew cab versions, with 34.3 inches of rear legroom in the extended cab and 38.7 in the crew cab, space is similar to Ford's F-150 and Nissan's Titan, and smaller than Dodge's Quad and Mega Cabs and Tundra's Double and CrewMax cabs.The crew cab rear seat is split 60/40 and can folded up individually for a flat load floor; this arrangement is optional on extended cabs.

Access to the rear seating area of the extended cab is eased by rear-hinged doors that open to nearly flush with the bed sides.Sitting in the back seat of the extended cab is made more pleasant thanks to the fact that the windows in the rear access doors power fully down.

The 5.3-liter V8 provided plenty of power for the extended cab SLE models we drove and the 6.0-liter V8 was more than enough for the SLT Crew Cab we checked out.All engines need to be revved up (by truck standards) for best grunt.Generally the Sierra models match competitors for smoothness, though by benefit of their five-speed automatics the Ram 4.7 typically runs with GM's 5.3, the Ram 5.7 and Titan 5.6 compete with the GM 6.0, while Tundra's 5.7 and six-speed auto performance can be matched only by the Denali's 6.2 and six-speed auto.

Of the suspensions, the Z83 is claimed the smoothest ride while the Z85 is slightly stiffer and for those who often tow moderate trailers.The Z71 is set up to enhance off-pavement driving.The Z60 configuration is for what GMC calls maximum street performance and includes big 20-inch wheels.The NHT package is designed for Sierra owners who need to tow and carry the heaviest loads.

With NHT, the SLT Crew Cab 4x2 is equipped with the Vortec Max 6.0-liter V8 engine, and a 3.73:1 rear axle.It was fitted with StabiliTrak, side-curtain airbags, a locking rear differential, and a convenience package that includes adjustable pedals, remote vehicle starting system and rear park assist.The SLT with NHT suspension is designed for maximum capacity trailer towing, with a special steering gear, shock absorbers, rear axle and tires.

The suspension is compliant relative to its carrying capacity but if you drive empty and don't tow you don't want to get the NHT package just so you can have the 6-liter V8 due to the harsher ride.Isolation and control are both very good but the best suspension setup for comfort on the widest range of surfaces is typically the Z71 package.

By virtue of its fairly stiff spring and shock rates, the NHT suspension can be driven aggressively on winding roads with tire squeal the primary indication you're approaching limits.Steering is direct by truck standards and nicely weighted, providing good feedback about how hard everything is working though the assist can fall behind during repeated full-lock maneuvering as when backing a trailer.

All new Sierras benefit from much improved brakes over earlier models, whether they have the rear discs or drum brakes.

For 2008, drivers who tow will appreciate the optional integrated brake controller like that used on the Sierra HD.However, be sure your trailer brakes are compatible with it before choosing the option, as some electro-hydraulic disc conversions do not work with the integrated controller.

The highest tow rating is 10,500 pounds on extended cab (not long bed) or crew cab models; top regular cab rating is 8900 pounds.Note these figures typically apply to a truck with just a driver on board, and vary substantially based on a variety of equipment and options.

G.R.Whale test drove various Sierra models and filed this report to NewCarTestDrive.com from California; with Larry Edsall reporting from Phoenix.