Ok, here's the deal with factory (narrow-band) o2 sensors. They only work in a narrow range around 14.7 a:f (this is for best emissions and decent mileage at low power). If you are on the lean side of that at WOT, I'd be VERY worried. You should always be on the rich side of 14.7 at WOT (way in the green). I think you need a LOT of tuning if you are getting lean readings on the guage, and you should definitely NOT beat on it until you do.