After taking almost everything apart in the transmission and steering, replacing a lot of o-rings, and waiting several months for back ordered parts (that didn't make a lot of difference), I am starting to think that the original advice of replacing the transmission pump ($3500) is correct. This is contrary to the advice given by the guy I hired to help me take things apart; He used a flow meter and said the pump was ok. Here are some related data points. I have only been using the dozer for about a week.
I over filled the transmission to see if there were any leaks that could account for air being sucked in. After 40 gallons of over fill, I stopped, and the dozer ran fine. However after about 45 minutes, the converter temperature started heading in the red zone. I drained 20 gallons, and the dozer could run for 2 hours without the converter temperature getting hot. 2 hours is about all I can handle in a single stretch, so I was fairly happy until yesterday, for the 1st time, I pointed the dozer with the rear end down hill. Right after that, the dozer wouldn't move. I bled the air out of the transmission filter test port (the oil was filled with a lot of air) and haven't pointed the dozer in that direction since.
So, it sounds like when the dozer's rear end is pointed downhill, the pump may have to do more work and can't handle it. But I want to make sure there isn't something else I can try before handing over $3500 for a new pump. I am still wondering how much oil I would have to add to get it to overflow and if that would show signs of leakage anywhere.