Ok I just replaced the water pump yesterday, but before then i was getting a SES light, it would come on and then go off well today i drove the it about 20 miles and the whole way it was getting bad acceleration, at about 2-3k rpms during take off and uphill it would cut back a bit. I got to where i was going and let it idle for a while and it said SES. Took it too advance and got code p0171, I need to know a good place to start as far as fixing it? the O2 sensor has never been replaced, It is a 2004 TB 4x4 4.2 I6 with 79K on it, any suggestions?