Is 4 catalytic converters realy nessessary?

I have a 2005 Tacoma X-runner. The 4.0 keeps throwing a code for the #2 bank catalytic converter is under required level and sometimes bank #1. Truck running fine. smooth idle, good performance.
I changed the trailing O2 and no change. I changed the forward O2 and then it tripped bad forward O2. Changed it back.
I can reset the code, then drive it and no code. I get on the freeway and drive 15 miles and no code. I park for an hour and get back on the freeway and the code comes back on.
I have replaced the plugs, the two trailing O2 sensors. Got a deal on to Toyota units. I have run Catyclean through it and no change. I have cleaned the AFS. The plugs concern me in that they are brown insulators and black around the edges which tells me it is running slightly rich compared to my 4runner 3.0 where the plugs are grayish white. The pic shows lighter than they are. Is this normal on a 4. 0? I like them to run a very light tan. What makes these run rich, it's all computer controlled.
Why are there two cats on each side. Can the second cat even get hot enough to keep the second cat clean? I changed the clutch a month ago and the cats looked normal with no debris in them.
Is there something on thee 4.0's that does this that I don't know about?

 

If you have not exhaust leaks and the O2 sensors are working properly then the converters have failed and will need to be replaced to get rid of the catalyst efficiency codes.

Converters eventually wear out, there's not really anything that will bring them back despite claims certain products make.

The P0420 and P0430 monitors aren't continuous monitors, they run when certain conditions are met and it takes 2 fails in a row to turn the light on so yes you can clear the codes and it may take a couple days before they come back.

The 2 downstream converters are not monitored so no need to replace them unless they are plugged or damaged.

Bad converters will not affect driving performance in any way unless they become restricted, melted, or break apart but this typically only happens when they have been overheated due to a misfire or other condition that causes excess fuel in the exhaust.

 

Could also be the leaking head. The early 2nd gens had a bad head gasket design

 

That looks very rich from what I have seen out of my 4.0L

are you supercharged?

 

nd4spdbh
Yes I also thought the plugs seemed very rich compared to my second gen 4runner. A rich condition could cause the converters to load up and throw a code. I just took it to Las Vegas and did not throw a code until a week after I came back.
I have replaced the plugs, the o2 sensors with new Toyota units and a new Map sensor (toyota) but it still throws a code after being on the freeway then shutting it down and starting back up. What will make these 4th gen 4.0 run rich? They seem to be very simple designed engines. The computer does most of the mixture control. Could the K&N air filter cause a bad mixture. There really doesn't seem to be much else on the system other than maybe a crank sensor. I am not as familiar with the 4.0 as I am with other Toyota engines. Any recommendations? I would hate to replace the converters if nothing is wrong with them.

 

If you're wondering about a rich condition just look at the fuel trims. At idle, while cruising and going up a hill under load