2001 Toyota Corolla P0171B OBDII code

Hi, the P0171B code - Bank 1 system too lean has come up again on my corolla. I had a 420 code and changed cat. converter, then had the uptake 02 sensor changed, the engine light went off and then came back on a few times after fueling with gas and finally now it is back on again. I now have had the fuel filter replaced and still the engine light is on and it is still not accelerating good when given gas. I have put in a couple of fuel injection cleaners and it gives a week of performance. However, this along with the check engine light has me worried. I was told after diagnosis it was the 02 sensor but I filled up with gas after it was put on which made the light come on. It has been reset numerous times and still says the same code 171 before I had the 02 replaced. What gives?
Please, Please help!