Just drove from Austin to Chilliwack, BC to pick up our new Escape 5.0TA fifth wheel. 2,500 miles up with out the trailer, averaged 22mpg. Return trip pulling the trailer averaged 14 mpg. Lots of mountain driving, and I drove the speed limit except in areas where it's 80 in Idaho and Utah, didn't go over 75. I'm sure holding it to 65 would have resulted in even better mileage.
The Ram tows this fifth wheel like a dream. On level terrain the truck drives literally just like it does without the trailer. On hills and mountain grades the transmission gears down but has tons of power, I did not encounter a single slope of any steepness at any altitude where I couldn't step on the gas and accelerate whenever I needed to. Passing a slow truck on a mountain grade while pulling a fifth wheel is a new experience for me...but I can get used to it!
The transmission really shines on long steep mountain downgrades. When I start picking up too much speed and brake to slow down it automatically downshifts to hold that speed and will not shift up a gear until I give it the gas again. And if I slow down further by braking more, it downshifts again. I had anticipated needing to use the gear selector buttons but never touched them once, the transmission always read my mind and responded perfectly.
The trailer is 21 feet, 4,300 pounds dry and around 5,000 loaded. Pin weight 700, my Demco Recon hitch 100, so with my 1,804 payload I still have 1,000 pounds left over for me, my wife, and cargo in the truck. I towed a small fifth wheel for 15 years with my 98 Ram and this is worlds different from that, a completely stress free towing experience.