Loss of power between 4000-5000
I have a 04 wrx 5 speed. I just noticed that at WOT my car will come into boost like normal then hesitate around 3,800 rpm then seem to lose all power until it slowly climbs to 5,000 then its like someone flicked a light switch and all power comes back until redline. Its always been somewhat unsmooth throughout the powerband but today was especially noticable (it was almost 90 degress today). I hooked up my glowshift boost gauge and noticed no boost fluxuations, it builds up to about 13 then drops to about 10 by redline. Ive recently replaced the fuel filter. The cars only mod is Invidia N1 catback. Thanks to anyone who can help.