All of this gets incredibly hard to sort through for the user between state and federal regs and manufacturer specs.
For instance, for a non-derated F350 Tremor, the 2022 Towing Guide states maximum gooseneck trailer weight of 20,000lbs and for a de-rated F350 it states 18,200 pounds with no mention of "Tremor". So add back the 1,300 lbs you're derating and you hit 19,500lbs. What happened to the other 500 pounds to get back to the non-derated Tremor, which is already derated by 200 pounds from a non-Tremor. Additionally, there is no asterisk and footnote for GCVWR for a de-rated F350. That number remains the same at 27,500, for Tremor, Non-Tremor, derated or non-derated truck. In a previous life, I was a CPA and this kind of stuff would have driven me nuts.
Hence, I hit on my solution. Derated F350 I'm within spec and legal under state law and federal regs on GCVWR and trailer weight and below CDL territory virtually everywhere. I'm busted on payload, but as I said, other than commercial vehicle weigh stations, I have never seen a cop weigh a rig in Texas, and to do it right they would have to split the truck and trailer to weigh each individually. Our local Barneys aren't going to work that hard, and I'm not even sure if "payload" is an enforceable term under Texas or Federal law. Maybe it is, I just don't know.
All that said, I wouldn't hesitate for minute to hitch up a 20,000lbs load if I needed to move it and if the law wanted to visit, I'm a farmer within 150 miles of my farm which is the trump card in Texas. Which would be true, for anywhere I am remotely likely to be hauling that much weight.