Ecoboost 3.5 Towing MPG Sucks

I have a son that drives 250 miles of interstate, each way, to go hunting here with me. He traded a 3.5 6-speed EB for his new 2.7 10-speed EB. Last time he came, we used his truck to go to my hunting area. I noticed he enjoyed using the power, and also the very high tech electronic radar detection mounted on the dash. I asked if the 10-speed improved his mileage, and he said no...still about 18 mpg. With 500 miles of interstate, speed limit 80 mph, but high dollar radar equipment still needed, I'm guessing, that he is keeping up with light aircraft.

I'm not a slow driver, but makes me wonder what the 2.7 EB would get for mileage, if I was driving?

Jerry