GCWR for a 3500 SRW GM 4x4 crew Dmax/A LTZ is 24500 lbs per GM online ordering guide.
It does indeed have a 42xx lb payload. Front axle is at 4486 lbs and the rear axle at around 2800 lbs. Of course these would be as shipped from the factory with the LTZ package and other options.
A couple of points about adding weight.
People in the trucks seats will add a certain percent of weight to the front or rear axle. The driver for example adds very little weight to a truck rear axle. Rear seat occupants add a bigger percent to he trucks rear axle. Same with a tool box/aux fuel tank setting in front of the bed.
Now the hitch is over the rear axle so 100 percent of it goes on the rear axle.
I wouldn't use another persons truck weights other than a guestimate.