I just bought a 03 durango and assumed it had the 4.7 because this is what was told to us but as it stands it is a 5.9 smpi (what ever this means) i would like to know what i can possibly get for mileage on the freeway (best results)..............thanks, Doug.

 

Well a cold air intake like a K&N air filter would be a start. Next change over to a fully synthetic oil. Change out those spark plugs with some OEM Champion plugs. Don't get the others. If you want some new wires as well. I prefer OEM.