New looks and interior refinements make the all-new GMC Sierra Heavy Dutys 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. 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 Dutys also come in a wide range of 2500HD (three-quarter 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 dualie for our test program.
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. The GMCs were high on everyone's list of favorites, with distinctive looks, quality interiors, and incredible powertrains. But did they rate high enough to raise the trucks to the winner's circle?
Click here to see an exclusive 2008 TOTY photo gallery of the GMC Sierra 2500 HD SLT & GMC Sierra 3500 HD SLT!