2008 Finalist: GMC Sierra HD
Tuner Numbers Straight From the Factory
By Scott Mortara

New looks and interior refinements make the all-new GMC Sierra Heavy Duty trucks serious contenders for our Truck of the Year competition--and they feature the most powerful diesels in this class.

All HDs come standard with a 6.0-liter gasoline V-8 putting out 353 horsepower and 373 pound-feet of torque mated to a Hydra-Matic 6L90 six-speed automatic. The 6L90 has a 6.04:1 overall ratio spread with two overdrive gears helping the HD's performance and fuel economy, but the cleaner, more powerful Duramax 6.6-liter turbodiesel engine is the real story. With the biggest numbers in the field, the Duramax puts out 365 horsepower and a massive 660 pound-feet of torque. A new particle-trap system helps provide a 90-percent reduction in exhaust particulates and a 50-percent reduction in NOx to meet the new mandates set in place early in 2007. Coupled to the diesel is the Allison 1000 six-speed automatic transmission, both of which now work in perfect harmony. The old school-bus transmission's hard, clunky shifts are replaced by quiet and smooth action.

The HD's ladder-frame configuration is reinforced by multiple cross braces in a segmented design that allows easy adaptation to the HDs' numerous lengths. Frame sections joined in overlapping segments bolster overall strength and rigidity. Because of this, Sierra HDs offer a larger 2.5-inch receiver hitch enabling the trucks to pull up to 13,000 pounds with a conventional trailer and 16,700 pounds with trucks properly equipped with a fifth wheel.

The HDs further offer two suspension packages: The Z85 suspension is standard on two- and four-wheel-drive models, while the optional Z71 off-road suspension provides additional chassis and suspension equipment, including skidplates. A high-capacity, four-wheel disc-brake system with Hydroboost and four-wheel ABS is standard across the range. All HDs are available with an integrated trailer-brake controller ($200) that automatically increases trailer braking when the truck's antilock system engages to prevent wheel slippage on the truck. The system eliminates the need to add an external or aftermarket brake controller.

Sierra Heavy Duties also come in a wide range of 2500HD (-ton) and 3500HD (one-ton) models in WT, SLE, and SLT trim, with three cab styles, three box styles, and five wheelbase lengths for a variety of configuration choices. There's a vast menu of interiors: Base and midlevel trims get a pure pickup theme, while premium interiors borrow the distinctive instrument panel and leather appointments from the Yukon SUV.

We acquired a Sierra 2500HD diesel and a 3500HD SLT diesel dually for our test program. The 2500 sprinted to 60 mph in 8.3 seconds, but we couldn't get a trailered run since this rig had no receiver hitch. The 3500 made the dash in 8.4 seconds unladen and in 19.3 with a 10,000-pound trailer. The 2500 stopped from 60 mph in 171 feet, the longest in the competition, while the six-tired 3500 only needed 152 feet.

In the off-road loop, the dually felt great through the sand wash, never giving the impression it might bury itself, but the 2500 didn't show the same confidence. The paddle shifters worked well in these conditions, with quick response to any required gear selection. Over the frame twister, the dually performed admirably, while the 2500 evidenced numerous squeaks and rattles.

The final part of our evaluation was a real-world road loop, where again the dually performed heroically throughout the drive--fun through the canyons, smooth on the freeway. One editor said he could see himself hauling his Ghibli to Monterey behind the dually. The 2500, however, drove big, wasn't as much fun as the dually, and rode rougher on the highway.

GMC spent quality time on the exterior styling to differentiate these trucks from those of Chevrolet. The Sierras have a single power dome on their hoods opposed to the double side bulges on the Chevy. The GMCs have a more wide-open grille and more natural-looking headlights along with smoother, more rounded wheel arches where the Chevys' are more angular. Even with those differences, GM has made it a point to make sure the Sierra and Silverado look similar where the Blue Oval is doing everything it can to make its vehicles look completely different.

The GMCs were high on everyone's list of favorites, with distinctive looks, quality interiors, and incredible powertrains. In the end though, they fell just short, as another manufacturer outdid most of the GMC's special talents.

What They Did Right
Both new six-speed automatics (one for the 6.0L gas V-8 and one for the 6.6L V-8 turbodiesel) are smooth and responsive, empty and loaded. Impressive, considering the workloads they've been hauling.

Room for Improvement
Engines are good but for a work segment as varied as the industries they work in, two engine choices aren't enough. These trucks want two diesel choices, and probably need two gas choices as well.

2008 GMC Sierra Heavy Duty
Base price range $24,860-$41,190
Model Tested GMC Sierra 2500 HD SLT GMC Sierra 3500 HD SLT
Price as tested $54,015 $55,610
Vehicle layout Front engine, 4WD, 5-pass, 4-door pickup Front engine, 4WD, 5-pass, 4-door pickup
Engine 6.6L/365-hp/660-lb-ft twin-turbodiesel OHV 32-valve V-8 6.6L/365-hp/660-lb-ft twin-turbodiesel OHV 32-valve V-8
Transmission 6-speed automatic 6-speed automatic
Curb weight, lb (f/r dist, %) 6844 (61/39) 7539 (57/43)
Wheelbase, in 167 167
Length x width x height, in 258.7 x 80.0 x 76.7 258.7 x 95.9 x 76.1
Actual payload capacity, lb 2356 3861
Max towing capacity, lb 13,000/13,000/15,900* 13,000/13,000/15,900*
0-60 mph, sec 8.3 8.4/19.3 **
Quarter mile, sec @ mph 16.4 @ 85.6/16.5 @ 83.5 21.3 @ 62.5**
Braking, 60-0 mph, ft 171 152
EPA city/hwy fuel econ, mp N/A N/A
CO2 emissions, lb/mile N/A N/A
VALUE ****
SUM UP Improved styling, powertrains, interior in both fit/finish and material quality as well as a wide range of vehicle configurations, means this is the right direction.
* Conventional hitch/weight-distributing hitch/fifth-wheel
**Towing 10,000-pound trailer