The stock blow off valve doesnt hold over 20psi very well so if you are boosting over that, that could be your problem.
I'm running a GFB on my setup and it works fine. I say buy a used blow off valve and swap it on. If it runs better with it keep it. If it doesnt, you know that isnt your problem.
Better yet, if you have someone local with an aftermarket blow off valve borrow his for some tests.
Hope that helps