I would suggest ignoring most of that.
It is entirely trailer/truck trim level dependent. You hook a 12.8k fifth wheel behind a diesel 2500 and you're almost certain to overload the truck. The pin weight alone will be in the neighborhood of 2,500 lbs, which far exceeds most diesel 2500 payload ratings. Most diesel 2500s have a payload rating in the 1,200 - 1,800 lb range.
The ONLY way you could ever hope to get close to towing a 20k trailer is a gooseneck flatbed where you can shift the weight back. Even then you won't likely get to 20k before either going over payload and/or exceeding the rear axle rating. For an RV... forget about it completely. The weight is static and you'll overload your rear axle long before 20k lbs.
The class V hitch is rated for much more than 500 lbs as well. Most have a 1,200 lb hitch rating.
That could be, I find it almost impossible to find actual ratings for tongue or gooseneck ratings on any of the RAM web sights.
The only things listed are axle GVW's, truck GVW's and supposed max trailer GVW ratings.
Such as this for my 2019 1500,
5.7L V8 HEMI w/ MDS 8HP75 8 Speed 3.92 truck gvwr 7,100 payload 1,780, base weight 5,318, front weight 3,165, rear weight 2,153, gross axle rating front 3,900, gross rear axle rating 4,100, Combined GCVW 17,000, trailer weight rating 11,240.
No where's do I see any tongue weight rating on the hitch or truck or online, must be they are afraid to publish that.