Early 722.6 transmissions had a poor valve body conductor plate design. This part has the starter lock out switch and a transmission VSS sensor built into it that powers the shift solenoids. I am not sure but could this be the problem.

Not hard to change the conductor plate you could do the job with tranny still in the car. Could it be possible that you have a leak in the A/T plug adaptor and it find it's way up to the electronic unit.