I have an old 2010 F-150 (last model year with the 5.4), so I get about 14-15 MPG on the highway when I have the cruise control locked on 60-65, and towing a 6500 pound trailer (5019 pounds dry... realistically with a battery, stuff inside and other items, I'd say with full tanks, I max out around the 7k mark.), I get definitely a lot less. I've experimented with towing using E85 for the added horsepower that booze gives... the resulting MPG was well within the single digits... but it did keep up speed even on the fairly gentle hills in this area.
I'm curious how the 2015 F-150 with the smaller displacement EcoBoost will fare when it comes to unloaded MPG versus hauling 5000-7500 pounds.
I do think it is cool how the "grocery getter" pickups (which apply to all half-tons) are able to tow a fairly decent trailer these days. I wouldn't want to try hauling a fifth wheel with one, but a TT for 1-2 people, it can do the job, as well as work in town as a daily driver.