5.0GN tow

I pull 8k or more every weekend all over the midwest, central south and eastern states with my 5.0, and usually get 11 to 12 no matter what running 70mph. Its a GN 3h sooner trailer with E load range truck tires on 8 lug wheels.

Velosprout

1. Unless in very severe hills or mountains, turn on tow-haul mode and just drive. Let the computer do it's thing, and let it use 6th gear as it chooses.
2. The mileage depends upon your speed (I seem to get 12-14 at a steady 55 mph on two-lane roads, but it drops to 9.0 to 10 on interstates at 63 mph with a headwind, and even lower on hillier terrain. I suspect your mileage is the best you can hope for, and will fall even further if you lock out 6th gear. You have a lot of frontal area on the camper, and although rounded, still with nearly the aerodynamics of a flatiron. It takes a lot of fuel to fight all that wind.
3. The off-road menu is not a worthwhile tool in truck weight distributing hitch set-up. View the Fastaway E2 or Equalizer hitch set-up instructional videos from progress manufacturing online, and use a tape measure as indicated.
4. If you are pulling a camper, it's a pleasure trip. Slow down, enjoy the scenery, enjoy the torque and quality of your F150, and enjoy the drive. The towing itself (after the first few trips as you get used to it) becomes one of the joys of travel.

7aTm11

When I posted this, I had only pulled the trailer once (200 mi) and I was 65-70. I've since kept it at 61-64 and obviously my mpg is better. My tires are rated for 50 psi cold, and have put them at 48ish.

Ricktwuhk

Check the SPEED rating of your trailer tires.

smokeywren

Trailer tires should be inflated to the max PSI on the sidewall - in your case 50 PSI cold. That's not for MPG, but for heat buildup in the trailer tires. Heat is the trailer tire killer, so you want the max PSI you can safely have to cause the tires to run cooler.