GMPartsGiant.com offers the wholesale prices for genuine 2021 GMC Sierra 2500 HD Denali 4WD parts. Parts like Air Cleaner 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 6'6" BOX 3/4 TON, CREW CAB 8' BOX 3/4 TON.