I would decide on the trailer first. I purchased my 2500 only to find out my 5th wheel trailer puts me over the GVWR of 10K lbs. when loaded out with gear, a full tank of fuel and my spouse in the passenger seat. If you decide on a 5th wheel don't go by the manufacturers website on hitch weight because it's approximate and your actual weight will probably be more by a few hundred pounds depending on what options are included (2nd AC, larger fridge, etc). When you find the trailer you want get the spec sheet on that trailer which shows actual axle and hitch weights measured at the factory. My configuration does not overload the rear axle or tires, but I do exceed the GVWR (gross vehicle weight rating) by 400 lbs. And of course, when you add the 5th wheel hitch you increase the payload again and 4x4's are heavier because of the added transfer cases, and the Cummins adds a big chunk also. All of this reduces the GVWR of the vehicle.
Do your homework before you purchase anything. Understand the GVWR, axle ratings, tire ratings, max trailer weight, max combined vehicle/trailer weight rating, etc... Only then will you know the 2500 is the way to go.
Good luck..