You lower comp ratio with just gasket.
here is some charts from tomei
http://www.tomei-p.co.jp/_2003web-catalogu...B25_gasket.html
EDIT: personally, I would rebuild to 9:1 comp and get the ECU re-tuned since you are only chasing 250rwkw.
maybe it's the auto tranny slipping?
2k for a tuned unichip?
might as well get the emanage then!
They have a special ignition harness for the 34's now.