I was driving my jd 4020 and went down a very steep burm . after a little bouncing arround the tractor would not go forward or backwards ,checked if the fluid was low and it was ,although i had filled it up a few days before. the tractor in first gear and very low revs will slightly rock forward.is it possible hyd fluid got on the fly wheel /cluch plate and it is slipping? could the clutch alignment be out. The pto clutch seems to be working.