[71 super]

Couple of questions. Has the hinge on the top been rebuilt? If you lift on the rear of the door do you feel slack/loose? If yes to question 2 the hinge is your problem. The pins have only a nylon bushing to support them and these after 30+ years give up and cause all types of problems. Is the door GM or aftermarket? If aftermarket many of them do not fit the hole very well and require adjustments to the window frame to fit the hole correctly- i.e. removing spot welds and adjusting. Is the door original to the truck? Some doors just don't fit other trucks very well. Last one have the rockers been replaced? Were the door opening braced when the rockers were cut out? If not the opening could have shifted and caused the problems you are having. I hope that the problem is the hinge as it is a $6 fix and relatively easy.