Whats Your Real Weights? Truck and Trailer. The Real Deal

I have a Dodge Ram 2500 Mega Cab with a 5.7 Hemi and 3.7 gear(I think) and have been told I could tow from 8100 lbs. to 10,150 lbs. How do I find out what the real truth is? Is there any book or link I can access to find out what I can truly tow. Am in the market to purchase my first 5th wheel and would like to know how I can get one that is not going to burn up my engine or tear out the rear end of the pick up. Any help would be appreciated!!!!!