i love being rite lol
basicly the MAP sees your boost, if it goes over a set PSI (i think its about 12PSI in a standard set up) it sends a signal to the ECU to bung it in to "safe" (map sensor will send a 5w signal to ecu once the limit is reached) with out wanting to sound bad, the remap hasnt been done fully correct...
normally the mapper will remove or change the limit to keep it safe.
a few things you can do, if you like the power you have and you have a boost gauge so you can keep an eye on things you can do a little mod on the MAP sensor, it involves putting a diode (like a resistor) in to the wires so the map sensor can only send a max signal of (for example) 4.7w meaning the car never thinks its over boosting, the n75 and maf can still keep things in check meaning boost still controlled and air is still being seen so no over/under fueling... i had to do it on my old LC as i had shat loads of boost issues this fixed them all BUT i also ran a Manual Boost Controller so i could set the boost to a set psi.
another option would be to set the actuator up (undo the 2 10mm nuts) as to me it sounds like its wound down to much, at oem spec the bottom nut should have 12-14 threads to the end of the rod (i think)
## personaly i think this is the issue as not many places set them up correctly and can cause propper fudging up of the turbo!!! best put to oem and left alone (rich coming from me lol)
what N75 are you running?