Bob its just not that easy to say what you will get. Each vehicle, while equiped the same will produce different results. There are tons of factors involved, air temp, clean air filter, tire pressure, stop signs, trailer wind drag....etc. I had an 07 fx4 set up for towing. I got better mileage with a heavy duty tandem axle with 4-5000 lbs on it than I did with my 18' pontoon. Wind drag murdered me. In short to answer your question I could only assume you would be in the neighborhood of 12-14 mpg's.