GMPartsGiant.com offers the wholesale prices for genuine 2021 GMC Sierra 3500 HD 4WD parts. Parts like Suspension/Rear are shipped directly from authorized GM dealers and backed by the manufacturer's warranty. Parts fit for the following vehicle options. Engine: 8 Cyl 6.6L, 8 Cyl 6.6L Diesel. Model Code: CREW CAB 1 TON CHASSIS 137.0, CREW CAB 6'6" BOX 1 TON, CREW CAB 8' BOX 1 TON, EXTENDED CAB 8' BOX 1 TON, REGULAR CAB 1 TON CHASSIS 137.0, REGULAR CAB 1 TON CHASSIS 161.5, REGULAR CAB 8' BOX 1 TON.