Catalytic Converter Code p0420 after wide open throttle

[MyExplorer03v8Lim]

Hello Explorers

Maybe it's just time for a new cat... or cats. The explorer has 160k on the body with 95k on the engine. I am pretty sure the cats are original.

Now the past two codes I have seen are P0420. Both times the code showed up it was shortly after a wide open throttle event lasting 5-10 seconds. To me the truck feels laggy on the throttle, there's a delay to me that others haven't mentioned.

I turned the first code off and it stayed off for 350 miles., until a wide open throttle event, and then I noticed the CEL lit a couple minutes later.

The thing that has me concerned, the vehicle also ran through a couple bank 1 upstream sensors recently, as well as a couple bank 1 coils, a bank 1 injector, and a bank two coil, as well as some plugs on both sides. I didn't see the plugs but I think they were junked from misfiring.

MY QUESTION
Does it make sense that it's only the cats that need to be replaced, or should I look upstream to figure out if there's still an intake problem?

ALSO
Should I replace all 3 even if only 1 is bad? What should I expect to pay, and should I do it or just pay someone (is it a giant PITA)?

 

[Hugh Janus]

Downstream o2 sensor should hold steady after ramping up. If it is jumping around like the upstream sensor then your pre-cat has likely failed.

 

[MyExplorer03v8Lim]

Downstream o2 sensor should hold steady after ramping up. If it is jumping around like the upstream sensor then your pre-cat has likely failed.

Thanks. Can I test this in neutral/ park in the driveway or do I need to be driving? I think I can use forscan which I've got on my laptop from when I programmed some keys.