Fuel filters in my manual are every 15000 miles. Air you tires up to max on tire sidewall. Run some state highways (read <65 MPH ) for a tank of fuel and see what your results are. Bigger tires and speed will kill your mileage. I think with your setup and >70 MPH your getting pretty good mileage at 17 MPG. Also the smoke is probably from the Bully Dog, if you set it back to stock and the smoke goes away under normal driving that's it.