When your pin weight and passengers brings you close to your maximum payload capacity with the truck, aside from air bags to help level, what's the #1 thing to do to add a little more safety? Tires? Would tires be the weakest link, before axle? What about wheels?
The RAM rear air covers suspension issues. You might install a set of 19.5" rims and tires when towing and put OEM wheels and tires back on for other times. As I posted on RV.net, the 19.5's have a higher minimum inflation. Maybe someone will come along and post about ride empty with them. You sure are rope-a-doping the issue.
Depending on you state you may have to license the truck for 14K.
Pin weight is the issue, not the trucks GVWR. Like I have responded a few times in your treads, I towed a 16K 5th wheel for to extended round trips to Az from NW Wa and did my homework choosing a 5th wheel with a 2435 lb dry pin weight(which I verified with Heartland). We had a Cardinal 29' for 11 years and found that only the smallest Cardinal and also Montana line up had light enough pin weights to match up the 2015 RAM Laramie CC 3500 4x4 SB truck we already had. Cedar Creek had a model that would have worked, however I did not like the interior.
We traveled heavy, full timing in the Big Horn for a year and a half. I knew going it that I could not add a washer/dryer and generator and stay under the truck's 7K rear axle rating. The LT275/70R18E tires along with the OEM 20's are rated to 3640 each, so there is NOT a lot of extra capacity there.
So, it boils down to that 2600 number that manufacturer is fuzzy on, and what you want to add to the trailer that will increase pin weight.
Given all if this, I have been in the same AZ RV resort for 12 winters now, I have seen lots of SRW truck arrive year after year that I know are well over their trucks manufacturers ratings and in a lot of cases over their tire ratings.
You can buy the trailer you want and set it all up the way you want it, and hit the scale. Then decide if you need 19.5 wheels and tires.
My recommendations:
Pucks
Aisin
Rear air
18" OEM wheels and tires
I would also add that we towed the Bighorn in very windy conditions several times without issue. DW decided that she was not comfortable traveling with the 39' foot fifth wheel back and forth to our AZ park model, so it became our Northern home and we bought a commuter trailer.