Reference Picture - Duster/Demon

Are both doors sticking, or just one? If it's the drivers side door, try taking the latch mechanism out and cleaning it really well to get all of the old caked up grease and grit out of it. Then lube/grease it up real good before you reinstall it. Just be careful of greasy fingers in the door jamb when you put it back in, cause that will make the paint fish eye when it's sprayed. Most cars, out old ones included, the drivers door gets 90% of the use. It may just need a little love to get it to act right.