If its to full you can get a foamy fluid which makes them act funny. 400's are tough and its pretty hard to hurt one. Try changing the pan gasket, governor gasket, and the speedometer gear adapter o-ring. Any one of the three could be leaking. Add fluid slowly tills up to the full mark when cold, or full mark when hot, some have both marked. It should hold about 11 quarts when dry, but just dropping the pan will be around 6 or 7 quarts. Start with five and add if needed.
Joe
