ok first of all if your o2 sensor is fluctuating at all, between .1 to.9 then it is ok, failure is usually a steady reading of .5 as that is default. for your latest problem try tapping on the FPR with a wrench while Fuel pressure is low and see if it doesn't change, if it does replace the FPR. In tank pump can be checked by performing a voltage drop reading at the fuse. if it is 1-3 amps it is probably ok,however there is a rubber hose connecting the pump to the fuel level sensor that can disintegrate and cause the problem when tank is below 1/2 tank. hope this info helps.....good luck!!