ECM - Difference between EM7747 and EM8747

[BuiltToWork]

I have an 1990 K3500 Auto 454 and suspect the ECM is bad.
Looked up the part numbers and these two come up:
EM7747 and EM8747
Took a picture of my ECM EM8747 but am curious if anyone knows the difference between the two.
My guess:
A/C control or Federal Smog or Man Trans vs Auto Trans.

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[PlayingWithTBI]

A/C control or Federal Smog or Man Trans vs Auto Trans.

Yes, TH400 (8747) to 700R4 (7747) auto trans. The 8747 will work with a 700R4 but, you won't get TCC. I'm not sure if a 700R4 (4L60) ECM will work with a TH400 (3L80) and it's kick down controls.

 

[BuiltToWork]

Thank you Peter. I am using the info you guys are providing to build a knowledge base of every part on my truck, before I tear it apart and re-built it. I want to know everything I can know about each part. I have a text file for each part and will post it in the "Build" section when I finally start my project. Have about 12 complete now. Plus I need a new roof on my shed/barn/garage building before I start.