Finally got the answer to my mileage problem and I got it the hard way. Pulled into my son's house and unloaded the trailer. Few hours later went to get something from the store and the pickup rattled, ran rough, blew white smoke and had almost zero power.
Had it towed to the Ford house and guess what? Two injectors went south. Began to trace the problem back and found the fuel pump also was only putting out 40 lbs. pressure. Replaced all that and the Techs looked at what caused the problems in the first place and found filter full of water, then traced back to fuel tank. Pulled the tank to clean it and it was filthy with debris. Very expensive fix, however, since I have run solo and got 15.6 where as I had been getting 10.5.
Leaving in a couple of days to tow and I'll see how much it changes the towing mpg.