The Sierra 2500HD 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 an 8-foot cargo box. The Sierra 2500HD is available in regular, extended and crew cab body styles. The exterior also features larger door handles, a new grill, hood and front fenders. Its tailgate has also been redesigned to make it easier to use and remove.The GMC Sierra 2500HD is all new for 2007.