I drive a yard tractor at a Walmart warehouse for a living. The Ottawa terminal tractor I drive gets Mobil Delvac 1300 super @500 hour OCI's. The engine in the truck is a 5.9 cummins, very similar to whats in the Dodge trucks. The truck pulls 44,000 pound trailers all day long. If you dont think these trucks work hard, try to get less then 4 mpg like I get. The engines last over 30k hours, we had one go for over 50k hours. If you want it to last forever, dont concern yourself about what oil to use, get a engine preluber. If you are lucky and live in certain areas, the supertech oil, if in the likewise bottles as mobil, is made by exxon-mobil at their Paulsboro, NJ refinery.