I'm not sure what year your car is? but if is a third gen, it's rpm max hp output is about 45-4800rpm's, lt1, around 52-5500rps?? I think on the lt1. I would guess either one of two things. First, spark/air/fuel. If you have the stock cam, you probally have the stock fuel pump too? Change both. If you have an lt1, go with a lt4 hot cam! And a 255l/hr pump. I would bet you get a HUGE increase of hp with teh two mods! My situation, my car was crapppin out at 3500rpms. zz4 cam. I put an fmu in and larger injectors. PUmped up my fuel psi and i got a little resutls out of that. Changed my fuel pump adn WOW! Point, spark, fuel air!!!
what's goin on here! look at the big picutre! time for a cam and fuel pump! adn how much boost? IF you are gettin more than 10lbs of boost, get the cam with a LC of 114~

 

You need to monitor your boost and fuel pressure. Does you system have a blowoff valve? If so, it may think you are overboosting and opening. Does you ignition have a rev limiter? If so check that too. I had a problem with one of my Grand Nationals where one of the rubber tubes on the boost side was leaking at high boosts. I would rule out the obvious first. I have a vortech on my car(lt1) and at 5k with stock injectors fuel pressure should be 70ish
Best of luck, keep us posted.