[billydonn]

The stock steel insert in the bottom of the tailgate side that the bolt goes into will spin if you don't jam it with something like a screwdriver or sliver of wood. There may be a notch in the insert ("trunion"?) to help you jam it, I can't remember for sure. When you get it jammed good it may even be desirable to use an impact wrench to break the bolt loose. Try a soak with penetrating oil if necessary. I believe you can get the tailgate off by getting just one of these bolts undone... then the other is easier to get at from both sides.

When you put it back together use some anti-seize to help you disassemble next time.