I've had my 2011 F-150 EcoBoost 4x4 w/MaxTow & HD Payload for 1-1/2 years now and I love it. I bought it used. The previous owner ordered it from the factory on a lease, and the holes in the truck bed indicate he towed a 5th wheel with it. It's a Supercrew w/ 6.5' bed, so it's one loooooong truck! My Eagle TT is just under 30' long w/GVW of 8000 lbs. It pulls my trailer like a dream and I had no problems gaining
speed while going up some pretty steep inclines through Missouri on my recent trip from Michigan to Texas. I just gave the cruise control a little "foot assist" to kick it down a gear, and up we'd go. As others have said, the engine braking on declines is not the best, but my transmission has a manual override button on the tree, so I'd just hit the "- button" to force a downshift; then hit the "+ button" to send it back into automatic mode. I always tow in the "tow/haul" mode, and my mpg while towing has ranged from 6.5 to 9.5, depending on terrain and (mainly) head wind. Don't expect to get over 19 mpg highway when you're not
towing, though. That is, unless you want to drive 55 on the freeway.
The only complaint I have is that it is so long, I do have a little trouble getting into some
campsites. As everyone knows, state park campgrounds have notoriously narrow roads. If there's a tree, sign post, or shrubbery across from my pad entrance, I have some trouble getting my rig backed in. I've learned to select my campsites accordingly, and I'm getting better at backing with more experience. One last thing: in extremely strong side winds, I do get some side pull when a semi passes me. I purchased a second (left side) sway control bar, and that has made a huge difference. I also think replacing the "P-rated" tires with "LT's" sometime this winter will probably eliminate that completely.
In short, I love my F150 EcoBoost, and would certainly buy another. I do think I'd move up to a 250 or 350 if I ever got a bigger trailer. The stiffer frame and suspension would be needed to handle the wind resistance of a rig 35' or more.