My 2001 F-150 V-6 shows codes 171, 174, lean bank 1 and 2. I have changed fuel filter, all plugs, plug wire, MAF sensor, air filter, ignition coil pack and the light is still on. The idle is smooth and I don't hear whishing sound, so i don't think there is leak of intake gasket and I don't see any broken or loose tubes that connect to engine body. I don't know how to check fuel pressure and I wonder if it's O2 sensor. There was some hesitation which was gone after I used fuel injector cleaner. I also changed gast tank cap. The truck drives pretty well, and gas mileage is normal for V6--about --15 miles local driving. Please help.