GMPartsGiant.com offers the wholesale prices for genuine 2004 GMC Sierra 3500 4WD parts. Parts like Engine Block Heater 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 6.6L Diesel, 8 Cyl 8.1L. Model Code: 3500 REGULAR CAB.