GMPartsGiant.com offers the wholesale prices for genuine 2015 GMC Sierra 2500 HD Denali 2WD parts. Parts like Automatic Transmission Planetary Gears 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, 8 Cyl 6.0L Flex, 8 Cyl 6.6L Diesel. Model Code: 2500 CREW CAB STANDARD BOX.