A904 has reverse no foward

Are you sure the tranny was not overfilled? If the fluid gets aerated from the guts whipping it up, and that aerated-fluid gets into the circuits, I imagine it could do all kinds of weird things. At shut-down, the bubbles would burst, and you have a reset. Then it would take a while to whip the fluid around again at hi-way speed.
Overfilled usually pukes oil out the vent, tho
This is a theory