Have you tried to recalibrate the pot by going into the service menu and calibrating C2? I'd start there. It sounds like the pot is working but fell out of calibration.
Otherwise you can check analyzer 4.24 and 4.25 to ensure the voltage moves smoothly when moving the traction command handle. If it is jumping atound or not moving when twisting slowly then it is much easier to replace the fully handle assembly.
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