car falls flat on top end

[its turbo time]

ive got an 85 gn that when the boost kicks in it really starts moving, but then it seems to kind of fall flat once the rpms start getting high.

i haven't done much to this car yet, just a 86 ecm with a red armstrong 93 chip, chopped the exhaust off and put an open element air filter on her.

what do you guys think?

 

[Bryan C.]

Try new valve springs.