A few have mentioned the axle weight on the vehicle, but you really need to run the numbers and make sure you don't exceed gross vehicle weight rating (GVWR) and/or gross combined weight rating (GCWR). What I found during my search for a tow vehicle was I kept overloading the truck (GVWR) before exceeding the rear axle weight, fifth wheel towing rating, or the gross combined weight rating cited in the tow charts. Max tow ratings on the manufacturer charts don't account for the hitch weight, cargo, or total weight of passengers (usually only 150lb. for a passenger is included in the table's calculation), which is fine if you don't plan on bringing along any passengers or loading any additional cargo in the truck cab or bed.
I just purchased a Ram 3500, DRW, 4X4, Big Horn with the Aisin HD transmision and 3.73 gear ratio to pull a Landmark Savannah. The truck is capable of towing 23,430 (max tow rating), 14,000lb. of gross vehicle weight (GVWR), 9,750lb rear gross axle weight rating, and a gross combined weight rating of 32,000lb. The vehicle, people, hitch weight, and trailer pin weight = 12,225lb., so I can put up to 1,775lb. of cargo into the truck before I hit the GVWR limit of 14,000lb.
Finding a hitch for use with the factory puck systems is still a challenge. I ended up purchasing a Pull-Rite 20K with the frame assembly that fits into Ram's puck system.