Air/Fuel Gauge...

Ok, My a/f guage has beeen fuking with me lately. First all of, it doesnt go back and forth from rich to lean at normal driving conditions anymore. It also doesnt go rich when its floored but I have no signs of detonation and im not losing anypower. Infact, the car is running better tahn ever at 5psi. (boost controller is broken )The gauge does drop to lean when I take my foot off the gas and thats normal so what could it be? I re-checked ground and things. Everything normal. Should I be looking at my O2 Sensor??