The last time I put a converter (just a 2800) in one of my cars without getting it tuned, I had all kinds of tranny issues. I was burning out clutches big time as soon as I increased my HP levels a little bit.
I've been discussing this with my tuner (Jeremy Formato). He definately suggests getting my car tuned for the converter, if I get a converter (which I hope to get this winter).
He also really likes the Yank converters. He's tuned hundreds (probably thousands) of cars and he really likes the Yank converters (combo of street drivability and track use).