Nice truck Jerry, hope it works out for you. My '05 Super Cab F-150 has the 4.6L, avg 17 mpg. Pulling the boat doesn't effect the mileage at all, probably because I tend to take it a little "easier" when towing? I don't believe there's much difference in the two motors when it comes to mileage, unless you're towing really heavy loads. Best truck I've ever owned!