I'm looking at the 3500 now
Good choice for towing a fifth wheel.
Just so you know, I spend a year researching, reading, etc. before I bought anything including our RV. I knew absolutely nothing about RVs and how to tow them.
Forums were of little help, the few reasonable folks that tried to help were pushed aside by the big-mouths who knew everything and owned nothing. I'm not suggesting that happened here but it happened to me over at rv.net
Of course, car dealers and RV dealers are yes people, I think General RV would have hooked up our Montana to a 1500 if that is what I drove in to pick up the RV. On the other side, you have a facet that insists you need a dually with 4:10s to pull anything over 1,000 pounds.
What my wife and I did was visit campgrounds over the summer and spoke with folks about their RV, dealer experiences, and towing. Very eye-opening but also very educational. Campers are typically friendly and outspoken and shared everything. We learned from their mistakes.
Once my wife decided on an RV I had the weight information needed to select a tow vehicle. Clearly, the pin weight of most fivers put the TV in 3500 territory. What is left is SRW or dually, Aisin or 68RFE.
As anxious as I was to get a tow vehicle and picking up our RV I had to put my excitement to the side, I wasn't going to settle for whatever a dealer could find for me. I wanted specific options, the rear air leveling, RAM's fifth wheel prep package, cargo camera, Longhorn non-filigree seating, SRW, 68RFE. I had to order which also meant a better deal since the dealer gave me back 100% of the holdback. It was a long nine weeks but I'm in my third towing season and have zero regrets on the decisions my wife and I made.
The takeaway from my rant is get exactly what you want and if you have to order one to get it, do it.