I traded my 1997 F250 last year on a 2012 F150 with the 5.0L engine, 3.73 rear axle. It tows my Hawk 2h BP/DR trailer every bit as well as the F250 did. In fact, I consider it to be the best towing experience I’ve ever had, and I’ve been towing 2h BP trailers with 1/2 ton and 3/4 ton trucks since 1969.
The Ecoboost 6-cylinder engine is made for towing and is completely adequate for your purposes. The turbo engine (the 3.5L 6 cylinder) is a little more mechanically complicated, and some of us olde phartes prefer the (relative) simplicity of an old reliable, but technologically refurbished V-8 (the 5.0L), but either is totally adequate for your needs. The Ecoboost can actually have a higher towing rating.
I cannot begin to describe what a good job Ford has done with the F150 in meeting the market need for “lower-end” towing (meaning 2h trailer size). The thing has stability controls up one side and down the other. It’s the smallest V-8 I’ve ever towed with, but the transmission that it is mated with uses the whole range of gears smoothly and efficiently.
I found this review when I was considering this truck:
http://news.pickuptrucks.com/2011/02/road-test-review-2011-ford-f-150-xlt-50-liter-v-8.html
and I feel it’s a very accurate review of how the truck performs.
Oh, and about the flat vs mountain issue–I live in western North Carolina. When I leave my farm, I have a 5 mile climb in order to get anywhere, and the truck handles it just fine. Tow-haul mode gets me safely back down on the way home. Of course, I would not haul without trailer brakes, but I drive very sensibly and feel that the truck would handle many emergencies adequately.
I don’t have experience with what the Ram and GMC brands have done, but I would expect that their recent model 1/2 ton trucks are similarly capable. It’s a new day from the situation of five and more years ago when the 3/4 ton diesels became all the rage for any towing and the 1/2 tons got neglected. Today’s 1/2 tons can do the job with basic 2h trailers.