I'm going through something similar on my 1993 4T60E after having had a transaxle rebuild by an incompetent shop.
When I finally picked the car up, after like two months of it being in his shop, he...

After doing some reading here and elsewhere, I bought this:
15422
.. and it worked!
I just connected the Tx and Rx wires together and stuck them in the M pin, and the ground wire into the A pin.
...

1993 Oldsmobile Ninety-Eight. 3800 Series 1. 4T60E. 250,000+ miles.

Backstory: Had the car for nearly 15 years and over 100k miles. Have done all the repairs myself except the recent transmission...

Yeah so, I'm seeking to take advantage of your combined centuries of knowledge and experience while being able to contribute very little in return.

I've got a 1993 Olds Ninety-Eight with over...