[randy500]

This question comes up frequently, I will explain the problem again...your door latch is worn.
Inside the latch on the same shaft is a latch wheel, it has teeth similar but square edged as the teeth you see on the outside of the latch.
The door has a latch pawl that engages the hidden teeth and a separate lock pawl.
The latch pawl wears along with the latch wheel which puts it out of synch with the lock pawl.
You can remove the latch and grind some clearance into the lock pawl to correct the problem.
I bought a truck with a set of repro door latches installed and they seem to work fine.