I think the first time this problem cropped up was about 10 years ago. It only happened once, but I distinctly remember pulling on to a road from a stop sign and thinking "this thing feels really slow" but there was no stumble or anything.
The A/T Self test would give me rolling codes. Everything from OK, to 4,5,6,7,B,C,D and a fairly persistent ECU Code of 54 (no communication with TCU). I looked for corroded connections, bad grounds, unplugged and checked the 4 connectors at the back of the transmission, swapped in a spare ECU because I couldn't get my consult software to connect. When things were really bad my only forward gear was 3rd.
Eventually in desperation, I swapped in a spare TCU. All was cured! So the old rule of thumb that "it's never the ECU or TCU" from back in the day apparently isn't always true on 35 year old cars. I took the cover off of the bad TCU, and it look fine - but there are several capacitors on the board that I'd probably check if I was going to try to fix it.
Anyhow, I'm happy to be putting the old girl back together again.
