I bought a Ram 2500 4x4 after reading from folks here who said there would be no problems at all towing with it. (I couldn't find a new non-4x4 in my area, only rear-drive new trucks were duallies, only used RWD were super fancy leather $50k for a used)
Turns out, it's 5" taller at the tailgate than my old 2002 Ram 2500. This means that the 5th wheel was towing nose high, and also meant that the back of the bed was dangerously closer to the bottom of the overhanging 5th wheel - a little bit of tilt or tipping downward of the truck, and I'd be hitting that overhang.
I called Magnum Trailer, and they said they've modded trailers like mine before - they built a 4" lift kit out of I-beams, with crossed support bars in the front and rear. Magnum did a great job fabricating the life, which is welded to the frame. That was over three years ago, and several thousand miles of towing. It's worked well, but the trailer does sit 4" higher, so I have to keep that in mind when figure out what bridge height I can fit under (14').
Pics - (LINK