Like the Chevrolet Silverado, the heavy-duty version of the Sierra has a stiff ride and lacks the selectable 4WD system and stability control. The 2500 and 3500 HD models are offered in two- and four-wheel drive as well as the dual rear-wheel setup known as a ¿dually.' Three bed configurations are available: a six-foot, six-inch standard; eight-foot long; and the Dually. The standard engine is a 353-hp, 6.0-liter V8, and a 365-hp, 6.6-liter turbodiesel that delivers 660 foot-pounds of torque is also available. It can haul up to 2,200 pounds of payload and tow a heavy trailer, and it returned 13 mpg overall in our tests. The engine is punchy and not too noisy, and the Allison-sourced six-speed automatic transmission is smooth.