My '15 1500 with 5.7, 3.92 gears, 8 speed, is pulling a 24' trailer that weighs in the neighborhood of 6000 - 6500 lbs, depending on how long we'll be gone. It's running with 13% tongue weight, and using the Equal-I-zer brand hitch. It tows like a dream. The OEM rear springs on the Ram tend to sag more than I liked, so I've upgraded mine. However, even with that sag, the truck was rock solid under all conditions. Most of my towing is in the mountains of the northwest. I could and in fact did on several occasions make passes on two lane highways while climbing those mountains. Plenty of power available.
I have no experience with longer trailers, but would be willing to get close to 30' and 7500 lbs.
Many will point out the typically low payload on these Rams. It seems to me that this is the direct result of those soft rear springs. The axles themselves are rated to 3900 lbs each. I'm always butting right up against that payload or perhaps a couple hundred pounds over. I have no problem with that either.
Edit: I forgot to add mileage. It's usually right around 9 - 10. Sometimes better, sometimes a little worse. It's consistently 2 mpg better than the '97 F150 it replaced. I tend to tow faster than I should for economy too. I hate being that guy slowing everybody else.
