Towing 39 ft 15.5 k with 1ton Sw diesel - Mistake ??

There is no reason for a 5er to have 20% pin weight other than the manufacture can put cheaper axles/tires under it. Before I'd get rid of my truck I'd shift 1000 lbs to the rear, even adding a tool box on the back to put heavy things from the front storage areas. This ASSUMES you are not at the limit of your axles and tires.