The GMC Sierra 3500 HD is available in a Work Truck, an SLE, an SLT and a Denali trim. The standard 6.0-liter Vortec V8 engine's new camshaft profile helps the engine produce more torque lower in the rpm band, for improved launch feel and a greater feeling of overall performance when towing a trailer and at higher altitudes. This engine can also be configured to run on E85 when ordered with a Fleetside pickup box. The revised and optional 397-hp/765 lb-ft torque B20 biodiesel-capable Duramax 6.6-liter diesel provides even more towing capabilities and all engines are mated to a 6-speed automatic Allison transmission. The stiff, fully-boxed frame provides durability and improves the overall ride, while supporting increased capability. The torsion bar front suspension allows for a greater front Gross Axle Weight Rating (GAWR). The rear suspension uses wider leaf springs - now asymmetrical to reduce axle hop ??? that contribute to improved ride and handling characteristics and increased rear GAWR. Large 4-wheel disc brakes deliver smoother, more immediate and confident-feeling performance and diesel engines include an exhaust brake. Stability control, hill start assist and a trailer sway control system are standard on single rear wheel trucks. Available features include mobile WiFi, USB connectivity, rear back-up camera, Bluetooth connectivity, XM satellite radio, OnStar 9.0 and a navigation system. For 2012, the GMC Sierra 3500 HD Truck introduces two new exterior colors along with various changes in optional equipment. Cruise control and vertical camper style mirrors are now standard on the Work Truck trim. The Denali trim now comes standard with heated and cooled front seats and a heated steering wheel.