I have an evo 6 that has a problem where it fuel/boost cuts at around 10-11 psi it feels like your hitting a wall, it also kinda missfires on de acceleration when slwing down on the highway. Here is a list of mods

evo 7 block
evo 6 head
evo 8 turbo
evo 8 injectors
fenix front mount with stock piping
fenix radiator
550hp walbro fuel pump
38mm wastegate unplumbed
aftermarket dump pipe
steamtube extractors
alloy intake pipe to turbo with big pod filter, still using afm
3 1/2inch turbo back exhaust
turbosmart type 2 bov
hd clutch
ralliart ecu
gfb geforce 2 with 3 port mac solenoid

so far i have replaced spark plugs (gaped to 0.30) have turned the duty cycle down to 0.0 (wastegate pressure) that helped and it boosts good in 1st, 2nd gear and then starts to cut in 3rd and cuts at 10-11psi in 4th and 5th gear. Have checked the lines going to turbo and wastegate and they are fine, replaced the vacuum lines for the gauge, and bov. It is bypassed the fuel pressure solenoid and is not running the egr regulation solenoid valve (vacuum hose is just blocked on the intake manifold). The car has not been tuned with these mods so i am wondering if it is that it needs to be tuned but i dont want to take it for a tune and there be something wrong with it so thought i would ask first