Addressing some common misnomers of the P0420 code

Just had this light pop on… yay

 

I have had this P0420 code for awhile. I have a 2005 regular cab 2.7 4cylinder 4wd tacoma. It came on three weeks after I had my spark plugs changed with NGK iridiums. Truck still ran ok for about six months but eventually developed a misfire/loss of power type feeling. Took it to shop mechanic pulled plugs and they were shot with roughly 18000 miles. Now mechanic says I need new catalytic converters and he thinks I need a new fuel pump because its running lean and fouling plugs. He already changed front O2 sensor and he says it passed fuel pressure test but still thinks fuel pump is bad because I have 266666 miles and have never had pump changed. May have to give in and go to dealership and hope they know whats wrong.

 

Caligula, is there a voltage range that should be seen with the scan tool when looking at said O2 sensors? Let's say a 2003 3.4L V6, at temp and running live data. What should be expected to be seen on the bank 1 sensor, and the bank 2 sensor? I have been trying to track down the actual oem spec for this scenario and have been coming up short.