Rams Body Builders guide shows the 2500 Mega cab has a 6000 rawr. This will be on your drivers side door post.
The 6000 rawr on 3/4 ton Dodge Rams has been around for 25-30 years. The Mega Cab is a heavy beast. You have the truck so drop by a set of CAT scales and weigh your trucks front and rear axles separately.
I've seen some Mega cab owners report 3100-3200 lb rear axle which leaves around 2800-2900 lb payload before exceeding a tire/wheel or rear spring pack.
The axle is a 11.5" AAM with around 10800 lb rating from AAM. Dodge Ram derates it with smaller tires wheels and rear suspension.
There are no 3/4 ton LDT that can handle a 16k lb 5th wheel RV trailer that can have 3200-3800 lbs of hitch weight alone. Add the hitch and other gear/people and your overloaded.
Many mod their 3/4 or one ton srw trucks with rear leaf suspension with 19.5" tires/wheels. The 2500 Ram has rear coils but I'm not up on rear suspension help for coils. Others may know.
I pull a '97 28RK 11400 lb 5th wheel trailer (31' 10" length) with my old '03 2500 Dodge/5.9 Cummins quad cab short bed. The truck has the same 6000 rawr and is well under all axle weight ratings and tow ratings.
Your payload is a GVWR based payload. Some 3/4 ton trucks with high gvws may show a 3500-3600 lb payload sticker which over loads rear suspensions. Other trucks like yours with a low gvwr = low gvwr payload.
I would be looking for a one ton drw for a 17 lb 5th wheel rv trailer.
