I wouldn't try jacking on the door opening. You'll never know where it will "give", and that would probably tweak something that you didn't want.
Is the truck original or a prior restoration? If the latter, someone didn't do the door fitting job right if body panels were replaced.
You probably don't want to mess with the paint, but the proper way to fit the door would be to grind some off the rear edge and re-weld the edge.
