GMPartsGiant.com offers the wholesale prices for genuine 2012 GMC Sierra 3500 HD 4WD parts. Parts like Engine Block Heater are shipped directly from authorized GM dealers and backed by the manufacturer's warranty. Parts fit for the following vehicle options. Engine: 8 Cyl 6.0L Flex, 8 Cyl 6.6L Diesel. Model Code: CREW CAB 1 TON, EXTENDED CAB 1 TON, EXTENDED CAB CHASSIS 1 TON 161.5, REGULAR CAB 1 TON, REGULAR CAB CHASSIS 1 TON 137.0, REGULAR CAB CHASSIS 1 TON 161.5.