Do you know gearing your truck has? CCC weight? (Yellow sticker inside drivers door). Ford produces ECOs for high gas mileage......OR.....pulling / hauling.
I have the 6.5 foot bed (see sig) and with my dry weight TT at 5748, I estimate loaded weight at 6500lbs. I don't carry water, wood, generators, four wheelers, etc.
My combo is very smooth, quite and without issues. Here in the flats of Florida I average 9.5 to 10.5 MPG @ 63 MPH. 63 MPH just seems to be a smooth comfortable speed for me while I'm towing.
Again, check your tongue weight with your CCC.
Good luck.....Happy camping!
2012 Ford F-150 Ecoboost, Screw, H/D, 3.73
1930 lbs CCC
2010 Flagstaff 26 RLSS (Sold 05/16)
2014 Jeep Rubicon JK