Unless you've been living under a rock, you know there's a war raging in the heavy-duty marketplace. These are the vehicles designed and sold to do the heavy lifting for job sites, contractors, and even toy-hauling families. If you have something to tow or carry a burdensome load, this is the segment that's battling for your attention. And this year, all three heavy-duty truck manufacturers are coming out with something new. Ford upped the ante first with the introduction of the F-450 Super Duty, then Dodge showed its Ram HD 4500 and 5500 chassis cabs, and now GM has just released its 2007 2500 and 3500 Silverado HDs.

As a follow-up to last year's half-ton Silverado (our 2007 Truck of the Year), GM is introducing the more rugged three-quarter- and one-ton versions, with many of the same exterior and interior design cues.

Unlike Ford's strategy of visually separating the light-duty F-150 from the larger and stronger Super Duty F-250, F-350, and now F-450, General Motors is keeping its pickup-truck line visually connected, no matter what the maximum trailer rating. You'll notice a similarity between the half-ton and heavy-duty's hood and body panels. The Chevy has a wider and taller dual-port grille, similar in shape to the half-ton's. Likewise, the hood has two muscular bulges running down the length, ending at the rear corners with a ridged, plastic covering (that includes a label identifying the engine inside), and it does offer some venting through the hood. The GMC grille has a wide mouth ringed in chrome with a prominent GMC emblem in the center. Its hood has the familiar half-ton power bulge, flanked by a jeweled headlight surround.

Engine choices have been simplified to include one gas and one turbodiesel motor. Gone is the old-school Vortec big-block 8100 altogether, while the new Gen-IV OHV 6.0-liter V-8 is the gas engine of choice. Now with variable valve timing, the 6.0-liter produces 353 horsepower and 373 pound-feet of torque, both at 4400 rpm. Don't be fooled--this isn't just a warmed-over version of the same VortecMAX engine GM's had lying around. This is the industry's first application of a mass-produced overhead-valve V-8 that can adjust cam timing at the same rate for intake and exhaust. The result is more power, better fuel economy, and a small-block V-8 that's about 90 percent cleaner-burning than the comparable engines of just 10 years ago.

This engine also gets a stronger version of the Escalade and Yukon Denali's 6L80-E transmission--now called the 6L90 six-speed. The new transmission has a 32-bit electrohydraulic control module to ensure smooth shifting as well as offering a Driver Shift Controller for thumb-controlled tap-up/down shifting. The system has a Tow/Haul button to help with grade braking and holding shifts longer when loaded.

On the diesel side, the 6.6-liter Duramax turbodiesel V-8 remains the tool of choice for more than 60 percent of heavy-duty buyers, and this latest version has a few improvements: It now runs on ultralow-sulfur diesel, the cylinder block is strengthened, the aluminum heads revised, the variable-fin turbocharger can react faster, the pistons are now aluminum, and, to meet the new 2007 federal emissions regulations, there's a sophisticated series of particulate filters that collect soot and other emissions. These upgrades allow the Duramax to offer a segment-leading 365 horsepower and 660 pound-feet of torque and to be among the cleanest diesels ever sold in the U.S. Of course, all this power and new technology comes at a cost: The diesel option is $7185, plus another $1200 for the mandatory Allison 1000 six-speed transmission. Like the 6L90, the Allison also has a new 32-bit controller to keep the shifts between gears smooth and solid. This transmission also has a Tow/Haul button that can hold gears longer when accelerating under load and downshifts sooner when braking. Additionally, the Allison can be manually controlled with a thumb-shifter on the column stalk. Those who tow (or race) will love this feature. We worked the gas and diesel's transmissions hard under full payload and empty conditions and found the shift hits surprisingly comfortable when empty and responsive when hauling and towing.