I know a few people that have run the TB spacer from cfm-tech.com, they designed this spacer just for the gm tbis. everybody i know that has used this spacer has loved it. and its the one i'll be installing on my truck when the 400 goes in. Another fairly cheap performance mod for the TBIs is an adjustable fuel pressure regulator. GMs stock specs are anywhere between 9-12psi is good. I know its been proven that even with a stock engine the tbis like to see at least 13psi (the stock pump with support up to 14.5 reliably) and with any kinda mods like exhaust and intake they really want that extra fuel pressure. IMHO if your gonna mod a tbi you should have an adjustable fuel pressure regulator.

 

I'd have to see someonewith it first.