Could be the door alignment/adjustment is off. I'd take the striker out, and slowly push the door closed till the body lines match up. I had both doors off to repaint the truck, and getting them adjusted correctly is truly an art form (not easy at all IMO).
If you don't feel any interference, then your issue is probably the latch itself.
I had all sorts of trouble with my 92 RC latches too. They'd refuse to unlock in really cold weather, sometimes wouldn't latch, sometimes the release button on the door handle would stick in the down position, etc. I ended up buying new latches from LMC truck, and they work great.
Mitch