Very interesting hady. I would be checking hoist motor supply for irregular voltage, current and frequency(if ac only)to see any abnormal drive supply. You do describe a stop/start action as well so I would've swapped the encoders firstly then the drive before any other action. You have changed guides and sheaves and I hope you also (while your at it) checked all the bearings for any abnormality. Since you have done this are they adjusted correctly and your not getting a safety gear rub? Its unlikely but who knows.
Its a hard fault but to me it indicates a drive or encoder issue particularly if the lift stops and starts.
