This shares a lot of symptoms with a problem that I had which was discussed extensively in this thread:
https://www.fordbarn.com/forum/showthread.php?t=261057
and then more in this thread:
https://www.fordbarn.com/forum/showthread.php?t=273571
At this point we think the problem is with the valves. I'm putting parts together to conduct a leak-down test. Check out the thread to see all the steps we went through.