SR20DET 'Limp Mode' HELP!

[Bumder]

I Have bought a 1994 silvia s14 with a SR20DET engine conversion from a SR20DE (Whole new engine)

PROBLEM:

I have only just noticed this now,

But when I go full open throttle (foot to the floor) in first gear the car goes fine until I reach 4000RPM then the car goes into 'limp mode' untill the needle drops below 4000RPM. It just looses all power and happens every time I go over 4000
Its the same in second and third gear and so on.

No spluttering, no smoke, runs smooth when driving responsibly

Im not reaching anywhere near full stock boost

The ECU hasn't been tuned and I don't believe it needs to be for these mods.

Engine Mods are:

front mount intercooler
hks blow off valve
t28 turbo
3 inch exhaust from back of the turbo
500hp fuel pump
aftermaket injectors (not sure what cc as I didnt do it)

[hOngsterr]

is the bov vented to atmosphere or recir?
also you can check for boost leaks, those are deadly.

[Bumder]

The BOV vents into the atmosphere but it doesnt get to vent before limp mode.

Ill try check for leaks in all the hoses and re-clamp all the intercooler piping.