Question on BMW 3-Series E36 O2_Sensor

Hi to everybody, I have a good question about my 1999 M3 US version, the problem is that the car runs like 325i, no power, checked for the fuel pressure 3.03bar instead of 3.5bar, when give it gas after 3000rpm the pressure increase up to 3.4bar, release accelerator and drop to 3.03bar, replaced fuel filter, fuel pressure regulator and fuel pump and vacuum lines related to fuel pressure regulator, everything OEM, still the same results, checked for power on fuel pump, the same like on the battery 14 , 14.5 volts,
Besides that was replaced oxygen sensors bank 1,2 sensors 1 only.
Gas mileage is 16, 17 mpg city and 23mpg hwy, I consider that's little bit to much for M3 manual transmission.
Do you think that should I replace the other two oxygen sensors, post cat ?! Can they make this problem ?

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[Nick at Pelican Parts]

Post-catalyst oxygen sensors will not create a low power issue. Have to checked exhaust backpressure?

- Nick