Does it have a turbo? If not, you might want to think about adding one. Those trucks are a dog, and move up hills at the pace of volkswagon bus without one, loaded down even worse. Also, what coolant is used makes a difference since they can be prone to cavitation. Try oilburners forum for more info about those trucks. Cab and chassis trucks I assume are f350's so it should have the solid axle unlike the twin i beam 250's. The manuals are also a lot more heavy duty than the autos, I would assume its a manual.