Just wanted to post this update. There was nothing wrong with my Y sustain board or Y buffer boards. The problem turned out to be cracked solder joints on the power supply board. When the TV heated up for 15-20 minutes the brittle lead free solder joints would open up and cause a shutdown of the Vscan voltage.
I was first fooled into believing there was a load (Y sustain/Y buffer short). After checking the boards I could not detect a short so I brought the TV up slowly and got a picture. The power supply board shut down again after 15 minutes. The third time around the power supply would not boot up without the Y sustain power cable hooked up (so I knew problem was contained in the power supply board).
The brittle lead free solder joints and normally dull and cracks are very hard to detect. I solder sucked numerous joint before using a leaded 60/40 based solder. Now the TV works fine without shutting down.