I just went through this on my 65 Dodge pickup. There are likely a couple of potential causes. There are 2 main adjustments on the door hinges; fore and aft (usually adjusted inside the door where the doors mount to the hinges) and, on where the hinges mount to the body (these set the "in and out" adjustment for the door). Sometimes body mount fatigue can cause the problem you mention but the hinge position can also slightly move over time as well just through vibration. The hinges are easily adjusted. Just be sure to take the weight off of the door (I used a floor jack and a block of wood) and then loosen, adjust, tighten again and test until you get what you want or need.

- EM