Most Efficient .5 Ton While Towing

My daughter that is into horses has pulled her horse trailer about 15,000 miles with her 2013 Ecoboost. She upgraded the trailer last year from a bumper pull to a 3 horse gooseneck with living quarters and roof AC. She went with larger tires when the first ones wore out so the speedometer and odometer read about 3% low. She generally drives with the speedometer on about 70 and she reports 10 to 11mpg. She has made the trip from Pulaski to San Antonio several times where she burns multiple tanks of fuel and gets a pretty good idea of her fuel consumption. The trailer and truck are generally loaded with all of the stuff that she can fit in each trip. I showed her this video and her response was "they did something wrong". I have to say that from my experience I concur.