What differences between a 91 and 92 transmission?

1990 with a 1991 engine

Well, my transmission woes continue - (short version: trans worked before engine swap, slipped bad after, replaced TC, still slipping). While I can drive around nicely especially when it warms up, I end up shifting to neutral at stop lights to prevent stalling.
I have an opportunity to buy an ebay transmission to swap out.
The listings say a 92-94 transmission is different from a 90-91 (which I have). If I use the ECU from the 90 - why would a 92 transmission not work? ie What’s in a 92 transmission that isn’t in a 91?

Any thoughts are appreciated.

The 1990 to 1992 cars are basically identical.
1988/89 cars (3.6) are basically identical.
The 1993/94 (4.0) are basically identical.