Sounds like we basically have the same truck. 3.73 ratio and crew cab? If the weights you listed are dry weight you will be close to payload when you load the 5th wheel 'stuff' and the truck with the family. With either choice I think you will be within the specifications of your truck but then there is the 'experience' of the tow. My camper runs around 6500 loaded and towing it is a breeze; however, I've met a few hills where I wish I had the 6.4 or the Cummins. My wife wife and I have been looking to trade up and I'm sticking with a TT simply because I like having the bed of the truck for my racks with kayaks, honey wagon, firewood, table, chairs, grill, bikes, inverter, etc.(as pictured below). A 5er consumes the bed. All a matter of personal choice at this point I guess.
2015 RAM 2500 HD Crew Cab w/ 5.7L Gas
2018 SportTrek 290vik
Blue Ox SwayPro