The heavy-duty Sierras are designed for heavy towing and hauling, not ride comfort and handling. The 2500 and 3500 HD models are offered in two- and four-wheel drive as well as with the dual rear-wheel setup. Multiple bed sizes are offered. The standard engine is a 6.0-liter V8. We tested the 365-hp, 6.6-liter turbodiesel, which produces 660 foot-pounds of torque. It returned 13 mpg overall. Our 2500 rode very stiffly but could haul a 2,200-pound payload. The diesel is punchy and not too noisy, and the Allison-made six-speed automatic is smooth. ESC is standard on some extended- and crew-cab models. A freshening is due this summer.