[afinco]

When an engine overheats, that heat (in the form of energy) is transferd through the rest of the engine block. Behind the engine is the torque converter for the tranny. When tranny fluid heats up it becomes less viscus and looses it's ability to provide torque to the tranny. Because the fluid is hot and looses it's ability to provide torque, the bands on the tranny drum will slip causing the problems in shifting.