I can solemly say that i was in the same boat.
I had a dyno before and after the split dump was installed, and NO power gains at all, torque, etc, etc everything same, However i was getting a HUGE boost creep, after 4.5k-5k it would spike to around 14-16psi, to which i backed off instantly.
I changed to a TOMEI 1 piece bellmouth design and it made things ALOT better. I had my timing adjusted which made things alot better. Now it only spikes to 9psi or so max, which i figure is ok considering i dont use an ebc yet.
R33 25t manual
fmic,
full zorst with no cats etc
Boost tap set to 5psi(bought off SAU) turbosmart or something. works really well.
copper plugs.
I suggest checking your timing as well as it will play a small part.