94 Escort shift problems (A Real Challenge)

I have a 1.9 with an auto transaxle. If the car has been sitting, it will shift perfectly when first driven. After it warms up and you shut it off, it won't shift out of the low gears when you start it to drive it again. Only 20mph top speed. Let it sit for a while and try it again, the car shifts like brand new. I had the tranny flushed, changed the oil and filter. No change. Took it to a transmission shop for them to look at it and they had it for a day. They drove it around around and it ran fine. The car has 92,000 miles on it and does not get used much. Maybe 5,000 miles a year. Also the first time it acted up, the engine missed a few fires then it ran smooth and the car up shifted.