A 6.0-liter Vortec V8 powers single rear-wheel (SRW) and dual rear-wheel (DRW) models, and both SRW and DRW versions are available with an optional 365-hp 6.6-liter Duramax diesel engine for extra towing capacity. Like all Sierras, the 3500HD is available in a wide array of bed sizes, wheelbases, drive types and cab sizes, as well as a variety of trim levels. Safety features include driver and passenger front air bags, tire pressure monitoring system (SRW only) and four-wheel anti-lock disc brakes. The Sierra 3500HD has a redesigned bumper for 2010 and the 6.0-liter engine is now FlexFuel capable allowing both regular unleaded or ethanol (E85) to be used. Active Fuel Management, which increases fuel economy is also introduced with this engine to deactivate four of the eight cylinders when the vehicle is cruising and doesn't require the excess power.