2020 GM 2500 trucks can have a 6390 or 6600 rawr that will be carrying all the trailer hitch weigh....everything in the bed.
The 6390 rawr version is probably with the smaller 17" tire sizes and good for approx 3200-3300 lbs in the bed.
The 6600 RAWR comes with the larger 18"-20" tires and good for around 3500-3600 lbs in the bed.
You have the truck so like all truckers you need to stop at a CAT scale and get the trucks separate front and rear axle weights. Generally 2500 gm trucks rear axle can weigh in the 3000 lb range however its best to know exact axle weights for safety reasons.
Is your 12600 lb weight numbers the trailers gvwr gvwr or a brochure dry weight ?? Depending on how much CCC the trailer has it can be best to use the full gvwr.
