Greg
Curb weight is the total weight of a vehicle with standard equipment, all necessary operating consumables (i.e., motor oil and coolant), a full tank of fuel, while not loaded with either passengers or cargo.
Starting at 3,970 you need to add the weight of any options that were installed at the factory (i.e. skid plates and 4WD) or anything added by a previous owner, plus the weight of the towbar, plus the weight of any cargo you add to the GC. Easiest way to determine the weight of the CG is to go to a scale and get it weighed. This can usually be done for about $10.
I looked at the hitch on our 2012 2551 and the hitch is bolted to the frame. It looks simple enough to remove and have a higher rated hitch installed.
Barry