Runnin Away

I know i have a boost problem that is being solved tonight. Now my other problem is when under boost around 5-7 psi ( I can't reach any higher) i get this extreme breakup like misfire. But when i reach 4500 rpm and my boost tapers off to 0 psi. It accelerates so much better than when im under boost. I mean basically if I want to accelerate its faster with 0 psi than with 5-7 psi. Any answers as to why so? It makes absolutely no sense to me.