The Stovebolt Site Forums The Shop Area Interiors Passenger door lock mechanism extremely tight

I think the cure is going to be to find an original latch. Everyone seems to have issues of some sort or another with the repop ones.
Mine were a bit worn, but I opted to rebuild them (welding the worn areas and resurfacing) as opposed to buying repops.

On edit: I just took a look at my passenger side latch and saw some things you could try (after removing the latch.)
The lock plate is sandwiched in with the safety catch, which is kind of spring loaded and may be what's binding up your lock. The housing extends down over the lock plate on the inside of the lock and could possibly be bent out just a touch to free up the pressure on the lock plate. It's also possible that something is binding up the lock plate, which should move fairly freely when the latch is in the closed position. There's a spring in the way of movement if the latch is in the open position. Here's a couple of pics that may help. I don't think you have anything to lose by making adjustments to your latch.