Amazingly throughout the number of body style changes from '78 through '96, the tailgate remained nearly the same. You can swap tailgates between all of these years taking note of the following:
I've broken down the 3 major changes into their respective years.
78 - 79 Type A
80 - 82 Type B
83 - 96 Type C
If your swapping within the same "type" it's just a direct swap.
If swapping A & B you have to switch the glass and glass support brackets
If swapping B & C you have to switch latches and striker plates
If swapping A & C you have to switch the glass, glass support brackets, latches & striker plates.