same EXACT thing happened with my first FC. it was a 88 SE and automatic.

well after a few hours of trying to figure out why it was happening, i came across a 5speed gxl shell for $100. when i swapped the motor over to the gxl and the gxl tranny, i had no future problems. HOW? WHY? IDK!

does my answer help? no, not really. but it was interesting enough for you to keep reading, so i am satisfied