Wait, there's one thing you haven't told us: what is FULL BOOST? By that I mean, what does it make when you have the boost controller plugged in @6000rpm?
If you have 8psi actuators (that's a problem in itself, way too weak) and running it at say, 20psi through the boost controller, then the boost controller settings are the problem. I would assume that's a gain setting of some kind, sounds like it's letting the boost come on very very slowly after it starts having to bleed air out, which is causing it to climb from 8psi to full boost at a snail's pace.