Two weeks ago my check engine light came on and my 2000 Durango with the 4.7 started running rough and getting bad gas mileage. I checked the codes and the code that came up is p0171 which I believe was the 02 sensor from what I read. So I changed the sensor that was before the cat converter, left the one behind the cat alone. My rango started running better. It took about a day of driving around to smooth out the acceleration check engine light went off, and my mpg was where it was supposed to be. Then last night I noticed my truck started running rough again and check engine light came on again throwing off the same code. I'm stumped and I don't know what I should do. Could the new 02 sensor be faulty? Could it be something else? Because I don't get how it corrected the problem then go back to square one unless the 02 was faulty. Any suggestions anybody??