I have the Cummins in mine and it is awesome. The fuel mileage around town is about 16.9 usually and on the highway between 20.5 and once I got 23. When the motor runs above 2000 rpm the mileage falls pretty quickly. I have the 373 gear so I can still run around 70 mph with good mileage.I have driven it off rd. on the beach in NC and it did very well the motor has so much low end that it has no trouble at all. I won't take in the mud so I won't be able to report on that,it's to nice of a truck. I plan on keeping this truck forever and hopefully it will be the last p/u I ever have to purchase. I want a Challenger, Camaro or must. Once I pay this off in around 3 yrs.