Hi guys, recently got my 04wrx sl with ppp, only mods are stainless de-resonate pipe / back box and k&N.

I'm having trouble, only sometimes, when accelerating hard in 1st gear there seems to be a monster flat spot around 5500rpm, more noticable on corners! once cleared it will accelerate fine up to the redline.

Doesn't seem to happen when i roll the throttle/power on, only when i welly it.

Any ideas? Cheers, Jon