LOL...I have nothing to go off of except that. Your telling me that a unit with a documented dry weight of 12.3k and one with a dry weight of 13k, both GVWR of 16 are gonna be the exact same? That doesn't make sense to me.
On a RV forum your going to get answers of all kinds.
Always look at the trailer CCC numbers and dry weight and GVWR.
...You will not pull a trailer at its dry weight after loading.
...Most of the "stuff" we add in a 5th wheel trailer goes in front of the trailers axles which add hitch weight on the truck.
...Todays 5th wheel trailers can have 3k-5k CCC which most folks more than likely won't ever use.
Your 2500 GM truck has a 6200 RAWR that will carry a 5th wheel trailer pin weight plus the hitch and a percent of occupants/etc between the trucks axles.
Trucks carry weight on its axles/tires so pay attention to the 2500 small 6200 RAWR which includes tires/wheels and rear spring packs. Increasing tires capacity won't work unless the wheels and rear suspension also is uprated.
Many 2500 trucks rear axle can weigh in the 3000 lb range which leaves around 3200 lbs for its payload. Now subtract a 200-250 lb hitch and the truck is down to around 2900-3000 lb payload.
This is why its best to weigh your trucks front and rear axle weights separately....or as some RV folks do is buy a one ton DRW truck.