Trailer Life Article about GCWR...etc.

op wrote:
I don't think that is correct, The GCWR is not on any stickers on the truck, if I change my axle gear ratio from 3.73 to 4.30 according to Ford documentation my GCWR with go from 19,000 lbs to 22,000 lbs for my signature truck.

Also, "must not be exceeded" ...I would think the "must" is a little strong if is not a legal limit.

What say you?

I would say your thinking is correct.
NHTSA has commented before about placarding the vehicle mfg GCWR number...however their lawyers and the manufacturers commented that too many minor changes can affect a motor vehicles GCWR.
IMO a good example is Fords 2014 F150 towing guide with the 3.5 EB engine.
15 different GCWRs from 13000 up to 17100 lbs.
5 different gear ratios.
now throw in GCWR differences with reg cab vs super cab vs supercrew cab.
and 2wd vs 4wd.
and different wheel base lengths.

The truck makers GCWR isn't a enforceable weight number for obvious reason. Nor will a non commercial truck/trailer ever be weighed for a GCWR or GCW......unless the truck/trailer registering state has that requirement.

JMO....
GCWR means more to a small truck owner with a tiny v8 or v6 engine/3.08-3.23 gears/small auto tranny/etc....however to a truck owner, like the OP, not so much as evident of all those commercial haulers out here with the same F350 DRW/heavy trailers pulling at 35k-45k GCW....and do so for 300k-400k miles before major mechanical issues start popping up.