First off hi to all, this is my first post. I like this idea of an all subaru model forum instead of a model specific, I mean if there was ever a manufacturer that interchainged its parts, but i digress.
My susgestion would be to go to your local dealer and see if there are any ECU reflashes available that haven't been performed on your car. I know for the USDM foresters there is a reflash for this problem (hesitation, stalling and afterfireing, as subaru puts it), it usually requers replacement of the front A/F sensor, but you said it was recently replaced. And it seems to me that I've been doing more of these reflashes in the spring and fall when our gas seems to change, anyway hope it works out.