Chevy and GMC go heavy duty.

Gary White, GM North America vice president and vehicle line executive for full-size trucks, explains GM's full-court press this way: "Three-quarter ton pickups account for about 70% of the heavy-duty pickup market, and our customers have come to expect capability as well as refinement in these vehicles." As a result, GM offers a multitude of body styles, powertrains, interior choices, lengths, as well as panel gaps on the 2007 models that bring a new word to the heavy-duty pickup market: "flushness." "This is an important segment for us, and we intend to protect our position by offering trucks that have better fit, better finish, and are more robust than the competition," says White. The new 2500HD and 3500HD series trucks share many of the refinements and changes seen in their light-duty brethren, but add a few tweaks of their own. These include:

* A one-piece wheelhouse and inner box side for greater box strength.

* An all-steel dually cargo box with hydroformed steel outer fenders.

* "Low and forward" mounting for the instrument panels. The premium instrument panel is located 5.0-in. down and forward, while the "pure pickup" IP is mounted 3.5-in down and forward to give a better view out and a roomier feel.

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* Most gaps on the instrument panels are 0.5-mm. or less.

* Addition of a stadium-style rear seat that can be split 60/40, and folded up to create a flat load floor.

* Hydroformed frame front sections, a ladder-type mid section, and more robust cross members. "The frame will twist 7.0-in. from corner to corner in extreme conditions," says Dr. Terry Woychowski, vehicle chief engineer, GM Full-Size Trucks, "which keeps the wheels available when crossing culverts and similar terrain."

* An increased frame section allows body gaps to be reduced. "We reduced the gap between the cab and the box by 50%, and tightened all of the other body gaps to passenger car levels," says Woychowski. "This not only improves the looks, but gives us better aerodynamics and less wind noise."

* Use of the new Gen-IV 6.0-liter gasoline V8 (353 hp @ 5,400, 373 lb-ft @ 4,400) mated to the new six-speed Hydra-Matic 6L90. It has a 6.04:1 overall ratio and two overdrive gears.

* A cleaner Duramax 6.6-liter turbo diesel V8 (365 hp @ 3,200, 660 lb-ft. @ 1,600) and Allison 1000 six-speed transmission. This combination has a 19% engine speed reduction at 60 mph compared to last year's truck.

* A patented exhaust venture that fits over the end of the diesel's exhaust system to draw cool air past the exhaust opening. "This item lowers the exhaust temperature by a couple hundred degrees, and is a simple and elegant solution to what could have been a nagging problem," says Woychowski.

* Addition of a larger 2.5-in. trailer hitch receiver platform that allows the trucks to pull conventional trailers up to 13,000-lb. (16,700 with a fifth wheel hitch).

* A new recirculating ball steering gear for better on-center feel and return.

* Standard four-wheel disc brakes with ABS and an available integrated trailer brake controller.

* Front seat belt pre-tensioners that work with both the front and rear crash sensors. It is the first system in the segment to activate the pre-tensioners in a rear crash.--CAS

@ Learn more about the light-duty versions of these trucks at:

http://www.autofieldguide.com/articles/wip/1206wip01.html