98 Windstar Transmission problem

I would like opinions on what failure could cause the following symptoms on a 98 Windstar, 3.8 with AOD. The trans was professionally rebuilt about 15,000
miles ago and worked normally till today. The fluid is clean, doesn't smell, and is not low on the dipstick.
It drives out perfectly for the first few minutes. Then starts to slip no matter what gear it is in, and will never go into OD. If you stop, it acts like it's in neutral, then it catches but chatters violently as you drive away for a few seconds. Maybe/maybe not will shift and pick up speed if you really play with the throttle. Will not climb a hill at all, slips very badly trying.
Here's what I can't figure out.....if you turn off the engine for even a few seconds and restart, it will catch in gear and drive out perfectly with no slipping, shifting properly, and even go into OD. After a couple minutes, maybe a mile of driving, the cycle repeats and it starts to slip again eventually no longer moving. I even tried this at 40 MPH, shut the engine off for a few seconds, coasted and restarted and it caught and drove perfectly again.
The only thing that comes to my mind is something like a clogged filter, which seems impossible due to the recent rebuild. I believe that it can't be in the electronic controls since there's no check engine light, nor any stored coded when we had them read.
What can possibly cause this weird failure? Is this a known problem that's easy to repair? Definitely not interested in having expensive repairs done again.
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