1999 Chevy Silverado Truck randomly acts like it is running

Hi,

I have been having a problem lately where my truck will begin to sputter and looses all power. It generally will not die but if I push on the accelerator it will not go above 500 - 600 RPM and it gets real jumpy and backfires. With that being said it did die one time and would not restart for a number of hours. During that time when I would turn the key to the on position and I would hear a series of clicks from the fuel pump rather then the normal humm. I have replaced the fuel filter, plugs, wires, and used water remover in the gas tank (as it kind of seemed like a bad tank of gas even though it has done this for multiple tanks, it seemed to be worse after I just filled up this last time). So does this sound like a faulty fuel pump or could it be the relay? I am currently waiting for it to do it again to test my fuel pressure. One last thing during the time it died my check engine light came on and it stated that there was an error with the oxygen sensor, I reset the light and it has not come on again. If it is not the fuel pump could the oxygen sensor cause the truck to run like this?