put 727 together. slips 2-3

did 2nd work when manually shifted into second ? mine kicks down and works shifted into 2nd

Nope, no engine braking either and is what made me notice it really quick.
I seem to remember something about auto second vs manual second, but I can't remember what it was.
I forgot so much about these transmissions after 25 years it's ridiculous, but maybe Tracy can give you an idea.

Fishy68 is Tracy.