Will it buck like crazy when you go over 4k no matter how much throttle? Be hard to overboost when only give it 30% throttle.
Have any check engine lights? Did you buy the car modded? I would see if you have any codes that are turned off. Good ol fashioned reset after that and see if you have the problem, if it doesnt come back right away then maybe you need tuned. You should be fine with those mods on an 02 tho. Do you have a stock intake? I would try that and see if you still have the problem. I have an extra if you need to borrow it. Do a boost leak test and see what comes up.
Where do you live? I can hook up my laptop and see wtf is going on. It wont be until Monday because I am going out of town today.