I had trouble with the Ford AOD in a Town Car. I would keep the 5 speed manual and let your girlfriend drive it, leave the wife at home. Just kidding of course, but it sounds like more trouble than it's worth to change the tranny.

1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy