I can't say on the fuel mileage as far as my old truck was concerned. I changed too much at once to say for sure. We did install one on a customers tow truck and he claimed a 2 mile per gallon increase, but I can't confirm that. I changed my stock 17* pump off a superduty to an adrenaline because it would not keep up with my 180/100 injectors. Never had a problem one after the change. Mine was 7.3 not a 6.0 just as a note.