need help with 95 thunderbird codes

[95t-bird]

I have a 95 t bird lx 4.6 and the problem is that when you give it more than about 10% throttle it boggs and wont accelerate, but if i slowly give it gas i can bring it up to about 3000 rpms and can cruise on the highway at about 80
. I scanned it and the error codes are 1131 (lack of upstream o2 sensor switch, sensor indicates lean bank #1); 1151 (lack of upstream o2 sensor switch, sensor indicates lean bank # 2); and 0171 (sytem too lean bank #1). The guy who sold it to me said the fuel pump in the tank was going out, but that didnt make since to me because an electric fuel pump doesnt just gradually go out, i have driven it for over a year like this, they either work or they dont, right? Is this guy right or is it my o2 sensor? Thanks any help would be great.