I have had this problem for quite awhile, no other BB'er seems to have had this problem, so here goes.

I push the OD switch, light comes on, no upshift occurs. If I lift off the gas (clutch is still engaged, car is nominally in 4th gear) rpms drop, as if the car has a freewheel (A'la old Saabs), if the rpms drop a lot, there can be a rumbling, as if the trans is unhappy being overdriven by the car.

After 1-10 minutes, the OD shift in, everything is normal.

This problem never occurs in the winter (below 50). Does not happen if the car is in regular use, more likely to occur if the car has sat for a few days, epeciallly if it had been driven in hot weather.

I have checked all wiring, Changed the tranny fluid, check it for being full.....problem persists.

any ideas welcome................