97 gtp with mods hesitation when boosting

Well last night I installed a 3.3 pulley... never had the problem before this.....

already installed mods
PCM
Headers
Flow master 3 inch cat back
k&n
spark plugs less then a month
voltage booster

I get a ses light that blinks when it happens

blinking codes NORMALLY means misfires. That indicates, usually, bad plugs. BUT since you replaced the plugs less than a month ago, I would make sure the tune you got is a good fit for your car. Do you have a way of scanning and tuning? If so, there's a BUNCH of resources out there to help you, ranging from a few guys here to the DHP forum itself.

Blinking is misfires. You changed the plugs but did you change the wires? I'm betting you have a bad wire or two.