How many 02 sensors are on an 89 Chevy 454 dually?

Co% max is 1.5 my amount measured was was 2.91 on the idle test. At 2544 rpm.It passed everything else

ya, o2 sensor seems like a good place to start

Thank you very much

If not the sensor any other guesses?

if its not a bad sensor then something is throwing it off and its not burning clean, high fuel pressure (not likely unless you have modified it), leaky injector, timing issue, or the new cat isn't working as they should.

Thanks again.