Just to update. My tractor had a catastrophic HST failure. Only one that I've heard of. My dealer is going to try to rebuild the HST. Took forever for them to diagnose the problem. Still don't know how much it's going to cost.
To anyone who might have an idea about this. I was moving dirt and noticed a slight vibration at the bottom of the HST pedal, worked a little longer and it developed into a heavy vibration and noise and the tractor would barely crawl. The dealer has taken the tractor apart and can find nothing...