Look under your Bounder at the welded on frame extensions. They are part of the reason for the 3500# towing limit. Also Ford only rates the drive train for 20,500#. That's 17,000# load on the chassis and 3500# being towed.
Probably the worst link in your drive train is that ol soft shifting E4OD tranny. Banks makes the Trans Commander (or something like that) or you can firm up the shifts with $5.Ã˜Ã˜ worth of resistors from Radio Shack. If you care to play electrician, I can provide a wiring schematic to firm up the shift points.