Wow.
From all this talk about the speed sensor, it looks like I did the exact right thing (by accident) by replacing the speed sensor in the 540Nm blue tag with the one out of my '90's 610Nm black tag. This would explain why the plug was different.
I had called a certain ZF6 Doc about that different plug and he told me I could order a plug or a harness from GM. He didn't mention that the newer style speed sensor wouldn't work in my '90.
All of this info is *really good*, it should be saved somewhere over on the Registry Site, maybe in the Technical stuff?
ZF-Factor? Could you cut and paste this stuff and add it to the FAQ's or somewhere?