TRCM is right. Your truck has a couple of ratings here that have to be considered.
First is GCVWR - Gross Combined Vehicle Weight Rating: This is your truck with fuel, passengers & gear + the weight of your towed vehicle. You should not exceed that number.
Second is the GVWR - Gross Vehicle Weight Rating - This is your truck loaded with fuel, passenger, gear and tongue weight or pin weight.
Lastly is your payload rating, i.e., your truck empty plus fuel, gear, cargo and passengers.
The best way to get those numbers are to google 2012 Dodge Ram Body Builder's Guide. It will have a table showing you your specific ratings depending on powertrain, gearsets, SRW vs. DRW, etc...