The 2012 GMC Sierra 3500HD is a heavy-duty, full-size pickup truck, part of the third-generation Sierra lineup. There are two engine options: a 6.0L V8 gas engine delivering 360 hp and a 6.6L turbo-diesel V8 producing 397 hp. Both are connected to a 6-speed automatic transmission, with rear-wheel drive and optional 4WD. The Sierra 3500HD is available in three trims: Work Truck, SLE and SLT, each offering progressively more equipment and luxury features. Inside, you will find a functional cabin with modern tech features such as OnStar telematics and SiriusXM Satellite Radio. Though advanced driver-assist systems are lacking, the truck's sheer size and strength are its key safety attributes. Its towing capacity clocks in at an impressive 17,800 lbs when properly equipped.