GMPartsGiant.com offers the wholesale prices for genuine 2018 GMC Sierra 1500 4WD parts. Parts like Transfer Case Internal Components are shipped directly from authorized GM dealers and backed by the manufacturer's warranty. Parts fit for the following vehicle options. Engine: 6 Cyl 4.3L, 8 Cyl 5.3L, 8 Cyl 6.2L. Model Code: 1500 CREW CAB STANDARD BOX, 1500 DOUBLE CAB STANDARD BOX, 1500 REGULAR CAB LONG BOX, 1500 REGULAR CAB STANDARD BOX, CREW CAB 1/2 TON.