I have an 03 Evo, I've recently developed this problem. The car drives fine, no check engine light and no codes, problem is under WOT when boost seems to peak the car stops accelerating, under low or no boost it will continue to accelerate just fine. I'm still relatively new to evos and boosted cars in general but first thought is a boost leak. Anybody want to weigh in on this or give me a direction to look into?

 

is the car tuned? you may be getting fuel cut possibly, but im just trying to throw ideas for ya

 

check the plastic piece on the plastic inlet for the filter mine came loose when I first got my evo and had same problem it was sucking up to the hood under boost and the power would drop and would make a sound like a boost leak.