ok the first question that should be answeered is does the door line up with the cab?
if not it's in the hinges, pins or bushings.
if so then air leaks maybe be from something else, if it lines up then it's where it needs to be.
bed, is it lower then the cab or higher?
if it's lower could be bad cross sills or rotted out ones.
You could shim the bed up to correct it.
if it's higher then the cab most likely cab bushings are squished or gone bad, or maybe rotted. change them and see if that does it.