What modifications have been done to your car? Anything that would have to do with Air in, boost, fuel, exhaust etc. (not cosmetic, tires, transmission or suspension related)
I would log an event if possible un upload here. Your going to want to make sure you are logging DAM (dynamic Advance Multiplier), AFR (Air/Fuel Ratio) sensor 1 and 2, TPS (Throttle Position sensor), Boost, and Target Boost.
I would do a log going up hill and one on a straight away.
I wouldn't put in any more sea foam. Run 93 if possible.
Could be a boost leak or bad plugs.
05 WRX Wagon - 409 AWHP / 334 WTQ Wicked Matt Tuned