Thanks again everybody for the help. I think I found the problem. I cleaned the filter although it seemed very clean and checked fuel flow from the fuel cock, again no sign of flow problems. I then put everything back together and when I went to bleed the system I discovered the bleed valve which is supposed to be closed normally was partially open. I checked my owners manual and it states that if the bleed valve is left open it can cause eratic engine operation and stalling. So far it seems fine now, but time will tell if this was the whole issue. I ran the tractor about 45 minutes with no stalling.