GMPartsGiant.com offers the wholesale prices for genuine 2013 GMC Sierra 3500 HD Denali 4WD parts. Parts like Exhaust System 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: 1 TON CREW CAB, CREW CAB 1 TON, CREW CAB 1 TON 137.0.