i got a 94 GSR and my gas mileage went downt he drain...i recently did a tuneup and installed exhasut and a testpipe, but had some trouble with the testpipe and im afraid i may have jacked up the O2 sensor....now, ive seen new O2 sensors through honda for like 300, and cheap ones for like 30, NTK has a O2 for like 50 or 60 i believe, now the question being is that NTK one gonna do the job for my car or is it imperative to replace with OEM and waste all that money? ...thanx in advance