I had a 1999 Dodge(Ram)2500 with the 5.9 gas engine, purchased new, and used to tow my previous trailer, a 7500lb Sunnybrook 26cks. It towed that trailer just fine and went about 140,000 miles before I sold it to a friend who used it for another 6 years before trading it in on something else.
I averaged around 9.5-10mpg towing during that time and also about 14-15 non towing. It had plenty of power and never failed to start or run smoothly. I really liked that truck and would have purchased another but a great deal on my present 7.3L PSD came along and I took it. Have no regrets doing that either! :)
You can see both the truck and the trailer in one of the pictures in my webpage photos linked in my signature.
Barney