If you know that your engine is sound, and that you don't have any boost leaks yet you're not hitting target boost numbers, then your factory catted up pipe may be the culprit.
For those of you looking to upgrade the uppipe in your Subaru WRX/STI among other models, Invidia has provided us with their 304 stainless steel uppipe. These uppipes with feature a provision for your factory EGT sensor, therefore no CEL fix is required.
This uppipe will work with any turbo that can mount to the stock uppipe location. Expect better exhaust flow and faster spool up times. New replacement studs will be included.