I'll be here to help Bud. What I found odd was I installed 4 new O2 sensors then a couple weeks later an engine light said all four were not responding

 

I'm not passing judgment on the prudence or effectiveness of Plug Foulers. But the reaction is not warranted by the above diagnostic readings. And you have gotten some faulty advice about REAR O2 Sensor readings. (There is no 'hard fast' from rear O2 sensors that tells much without being thoroughly weighed against numerous factors. They must be warmed up to start working (arund 900 - 1000 degrees f). The PCM monitors them and compares the 'NUMBER' of voltage switches (across .45v) between the downstream and upstream O2s. Cat efficiency codes will be thrown if the Ratio of downstream to upstream switches EXCEEDS 66% or 75% -(depending on exhaust configuration). Holding steady around .65 to .75 volts represents ZERO % switch ratio and will NEVER throw a code. Basically speaking (though NOT conclusive by itself), a defective will exhibit voltage swings mirroring upstream O2 sensors.

O2 sensors "on our trucks" - (Not later model wide range O2 sensors) are VERY DUMB devices designed to effectively "create a short circuit to ground" when they see (smell) oxygen molecules. The PCM applies a current controlled and limited 'reference' voltage of One (1) volt to the O2 Sensor element. (NOT HEATER), that's separate. They have to be heated to work. The heater is used on upstream ones during early part of drive cycle to make them work until exhaust temp takes over the job. If they 'SMELL' NO oxygen, the current they draw is minimal and the standing voltage is 9 tenths (.9) of a volt. As soon as they smell Oxygen, they become a conductor (though a little slow reacting) and short the reference voltage to ground - essentially 1 (.1) tenth of a volt.

This can be verified by watching O2 voltage during an extended 'deceleration'. PCM will finally shut fuel injectors OFF and the engine becomes essentially an air pump. O2 sensors are FLOODED with Oxygen and the voltage on All of them will go to .1volt.

Point 45 (.45v) is considered the 'boundary' between smelling oxygen and NOT smelling oxygen. For Upstream O2 sensors, the Injector pulse width (subject to Fuel Trim adjustments) is constantly being varied up & down trying to keep the O2 voltage at the impossible threshold right between smelling Oxygen and Not smelling Oxygen (.45 v). When equal time is spent 'above' and 'below' .45 v, PCM has established the perfect fuel / air ratio and 100% of the oxygen is being burned in the combustion process.

As for downstream O2 sensors, their ONLY purpose in life are to monitor the health and effectiveness of the catalyst - which by design can 'store' some oxygen for a short period. When it does, any hydrocarbons reaching it (during brief periods when injector pulse width made fuel / air mixture slightly over rich) react with the stored oxygen in the CAT and "BURNS UP". Thus the downstream O2 sensor should not see the 'residual' Oxygen from the combustion process during injector variations. Remember - when it sees NO oxygen it is 'open circuit' and the reference voltage will be high - sensor is NOT shorting the voltage source to ground.

I know you didn't ask for all that. But thought it might be applicable to someone. Basically, if your CATS are plugged up - it is because the catalyst material has melted - and their effectiveness would have gone to hell. The rear O2 voltages would be more or less mirroring the upstream ones.

 

Cats are new. I'm lead to believe I'm having an electrical issue (based on quirky isolated unrelated usually one time each instances) but won't be able to report in depth until this timing job is done.
Your write up is greatly appreciated. I'll be re reading soon when truck is running so I can utilize TorquePro to the maximum. Thank You