So your trouble isn't necessarily a "drive" problem, but quite possibly the CPU-or something else (at least that what I understand so far).
Here's a wild one for you and I actually had this happen to a Swift Futura job I used to service;
I started getting this DPP count error in the up direction only at a certain position in the hoistway, shutting down the car when the undercount occurred more than three consecutive times.
I did everything I could think of to address the issue.
Turns out that two newly installed satellite dishes on the roof were the source of trouble. Dish wiring from the roof ran straight down the building interior wall, through a chase right next to the hoistway and at the trouble spot in the shaft, it was right on the opposite side of the drywall, OPPOSITE THE SELECTOR. What's that called...RF Interference? Once this was proved to be the problem, efforts were made to alter the dish signal proximity to the hoistway and trouble was solved. One of the weirdest things ever.
