2007 Chevrolet Silverado 2500HD Page 1

Who needs 660 pound-feet of torque? Someone who needs to drag 13,000 pounds around, that's who. And the only 3/4-ton truck that can tackle that job is Chevy's Silverado 2500 HD armed with the optional 6.6-liter Duramax diesel V-8, which drove — and admired — during a recent test.

Chevy's he-truck edges out the Ford F-250's 6.4-liter Power Stroke diesel, which has a maximum tow rating of 12,500 pounds and 10 fewer pound-feet of torque. And it out bench-presses the Dodge Ram 2500 even when that truck is ordered with the newly available 6.7-liter Cummins turbodiesel. (This new engine replaces the Ram's old 5.9-liter diesel and produces and impressive, but still second place, 650 lb-ft of torque.)

Both the Ford and Dodge diesels offer less peak horsepower, too. The Chevy's Duramax weighs in with a class-leading 365 hp vs. 350 hp each for the F-250's Power Stroke and the Ram's Cummins.

Another unique draw of GM's 3/4-ton truck is the heavy-duty six-speed Allison 1000 automatic transmission — a mandatory upgrade when you choose the Duramax diesel engine. This is an incredibly beefy unit designed to stand up to the frame-twisting output of the Duramax V-8. It also has different gear ratios designed to take best advantage of the diesel's massive low-end grunt. Since all 660 lb-ft is available at just 1600 rpm, the Allison's first gear ratio is 3.10 (vs. 4.03 for the gas engine's six-speed automatic) while fourth gear's 1.00 (vs. 1.15). And the final drive ratio with the diesel is 3.73 — vs. up to 4.10 with the 2500's standard gas-burning 6.0-liter V-8 engine.

The taller gearing keeps the diesel V-8 operating closer to its torque peak off the line and under hard acceleration or while pulling a heavy load, while also keeping highway revs (and engine racket) down. In sixth at 70-something mph, the big truck lumbers along quietly with the engine barely turning a fast idle around 1700 rpm.

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