The Sierra 3500 comes standard with a 312 hp 6.0-liter V-8 or an optional 365 hp 6.6-liter turbo-diesel. Both engines are controlled by a six-speed automatic transmission. It can be equipped with dual rear wheels and an 8-foot cargo box. The Sierra 3500 is available in regular, extended and crew cab body styles. The exterior also features larger door handles, a new grill, hood and front fenders.The GMC Sierra 3500 is all new for 2007.