Hello congrats on the new 5th wheel. The Ram 2500 is not rated to carry the pin weight of your camper.
I have 2014 Ram 3500, CTD, SRW, CC, 4X4, 68RFE with 3.42 Gears. My door sticker states I am able to carry 3,900 in the bed. Whatever truck you look at be sure to look at the door sticker. Different options will change the tow capacity, and all of the other measurements.
Also, the 4:10 I don't believe was an option with the 68RFE with CTD. You will have to get the Aisin Transmission to get the steeper gear or possible the 6.4 Hemi.
Good Luck! I love my RAM!!