I had the same thing with Ol Yeller (a '52 1/2 ton)about 2 months ago. It was as if it was welded shut. My daughter-in-law thinks old trucks need to be slammed around a bunch. Turns out the latch mechanism wedged itself over center. The only way to fix it was to take the inner window crank and door handle off. Remove the door panel and take a look at where the latch is. I found that I had to pry the spring off the latch to get the darn thing to come loose. This took quite a while and I had decided that if I had to buy a new one might as well just tear the whole thing out. As luck would have it after the spring was removed the door popped open. I put it all together and then spent some time re-aligning the door latch adjustment on the body. After about an hour and a half it works. Now when the girls go for a ride I let chivalry take over and open and close the doors for them.