I have a 2003 Sierra 5.3L that bogs down only on heavy acceleration, under gentle acceleration works fine, felt like a Cat to me, tempature tested it, right cat tested at a lower temp behind the cat, indicating to me that the cat was clogged due to no chemical reaction happening in the cat (i do not have a exhaust back pressure gauge handy). replaced the cat, code comes up (codes may have been there before, i didnt read them since one o2 sensor was broken and disconnected) codes are Bank 1 sensor 1 voltage low, Bank 2 sensor 1 voltage low. means its reading rich so im told. replaced the o2s incase faulty. still reads same codes. did a fuel pressure test, has good fuel pressure, does not drop with load.

throttle position sensor and MAP sensor appear to be working fine.

scanner wont read the EGR at all so not sure how to check that

My next step is to do a fuel volume test, ensure that 1L of fuel is being pumped out every 30 secs. possibly fuel pump and filter issue. not to sure

anyone else have any ideas?

 

I think if the voltage is too low on those O2 sensors, that means its running lean. Check your Throttle Position Sensor.

 

ya your right, low voltage was lean, i should have taken the 30 seconds to look it up on the computer, would have saved me a lot of headache.
problem is solved, clogged fuel filter. so simple yet took a day to find that out.