T-25 sputters at full boost

[Andrew9146]

I just got this car about a month ago. It had been modified but brought back to stock. Not sure what all was done, but the previous owner's friend worked at the dealer and said he had a different turbo on it. But he didn't know $&!# about it. Anyway, it ran fine till about 3 days ago, and now when I give it full throttle, it spools up and then between 4 and 5,000rpms it starts sputtering and then its fine. Under no load, the engine revs and sounds good, but when I get on it, it sputters pretty bad when the turbo reaches full boost. And its getting worse. Only mod i've done is an A'PEXi power intake system and A'PEXi turbo timer. But I just mad a 500 mile trip to Pennsylvania and back and it was fine. It started doing it shortly after. Could my turbo be bad? or do I need to look elsewhere? Also, the factory boost gauge does not work, and I just bought a new boost gauge, but haven't installed it yet. I KNOW I KNOW, I am doing it tomorrow, also bought oil temp and oil pressure gauges. Still need intalled. Can you help????

 

[exzercist]

maybe boost leak? what you boosting stock boost?