I have a unit doing the same thing. Only it does not shudder as bad as you are describing. Its always there & I can see the fluctuating amp draw in run amp draw mode. We swapped out control handles with another unit-still did the same. Removed the braking system-no change. Changed the drive motor encoder bearing-still same problem. Left it go for 6 months & now its becoming worse. We are now going to swap controllers with a known good controller & see what happens. (Our code is 33073 Control handle issue)
Did you find out what the problem was with the unit you have?