check the coupler that joins the POT4 to the drive unit for excessive wear.
it sounds to me like the coupler may be getting to much slack in it and causing it the show out of range.
if the coupler is ok and the problem keeps coming back you may have to swap the Access 5 out with a truck that is not having this problem and see if the problem goes with the Access 5 to the other truck. if the Access 5 turns out to be the problem keep in mind that the Access modules are usaually covered under warranty for 3 years or 3500 hrs which ever comes first.

good luck

bruce_c