I have read through the prior posts, but not found exactly the same issue.
I have a 1986 Chevy Suburban C20 3/4 ton with power windows / doors. The rear power window will go up and down most of the time, but occasionally the window will refuse to go up. I open and close the tailgate several times (checking to make sure that it's closed properly) and eventually it works, but this is taking longer and longer. Any ideas where to start looking for the problem?