or you could remove the pan, put a low presure switch in the 4th control valve, this switch will have 2 wires one goes to the lockup sol, the other will go to a 12 volt source external when the key is on, ground internally the other wire on the lock up sol, no when the car is in 4th gear only the tork will lockup. i do this lots for hot rods, works nice..the switch you need is in the older 700r4 trans like 82-83. units..