GMPartsGiant.com offers the wholesale prices for genuine 2020 GMC Sierra 3500 HD Denali 4WD parts. Parts like Automatic Transmission Oil Cooler Pipes 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.