MoparPartsGiant.com offers the wholesale prices for genuine 2018 Ram 4500 parts. Parts like Rear Door Trim Panel are shipped directly from authorized Mopar dealers and backed by the manufacturer's warranty. Parts fit for the following vehicle options. Engine: 6 Cyl 6.7L Diesel, 8 Cyl 6.4L. Transmission: 6-Speed Automatic Transmission, 6-Speed Manual Transmission.