wants to die at 4500 rpm at WOT

[98gstaherns]

I dunno what the hell is going on with my car but here is whats happing.
car 98 gst
14b
bolts on and mbc @12 or 15 lbs.
So heres the deal I just had some work done on my car because a exhaust manifold gasket needed to be replaced and so that was done and i was driving back on the freeway and wanted to finally be able to get on the gas and make some boost. Because it was a pretty bad leak and it wouldnt build boost very well. So Im at WOT and at like 4500 rpms the engine just wants to die it felt like it was bogging down and would go over that at all with out dying. I did notice this before about a couple weeks ago and figure it was because everything wasnt able to keep up because of the bad leak. Any input would be great thanks guys.