Cub Cadet Tank M54 stuttering or jerky on left side under load

My Tank would stutter, strong jerky action maybe 5 or 10 times a second. It only happened under load on the left side, when starting moving, uphill, on a side slope with left wheel to the bottom, etc. If I ran closer to 3700RPM than 3600RPM it didn't seem to happen as much. I figured it was a belt (slapping/skipping) or a pump/wheel motor problem. So I replaced the belt and nothing improved. That made me assume it was a hydraulic problem. I just kept using it until it failed.

This...

Cub Cadet Tank M54 stuttering or jerky on left side under load