Originally Posted by elongest
I have a 2015 eco diesel 6 ft. bed and had thought about a 5th wheel hitch. I did a quick check of Etrailer. It looks like they don't list a hitch for the 5 1/2' Ram and it appears they may have different hitches for the 6 ft. eco diesel and non eco diesel models.
In almost any modern pickup truck, despite the variations in cabs and boxes the truck is identical from the rear axle area rearward - all of the change in length due to different cabs and boxes is accommodated within the wheelbase. This means that the same brackets usually fit the same way regardless of the box length.
When retailers or manufacturers says that a fifth-wheel can only be used with a certain length of box, they are usually assuming a specific width of trailer (now typically 102", the legal maximum) and saying that there isn't enough clearance from hitch to cab to turn the trailer. Escape trailers are much narrower, so less distance is needed to the cab, and these blanket statements about usability do not necessarily apply.
I don't know what causes the dependence on the engine, but a reasonable guess might be that there is interference between the exhaust system and the mounting brackets, so you need brackets designed to fit with your exhaust.