P0420: Catalyst Efficiency

I'm running my 12 prius with P0420 staring at me from the dash. With some footjob p), I still manage to get 50+ mpg, coasting, gliding, downhill advantage, etc. I got the car with this code. Don't know the history. Here are my findings and actions:

1. The CAT temp is equal at both ends.
2. Downstream O2 sensor jumps up and down.
3. Previous owner replaced the O2 sensor within 6 months.
4. I replaced the PCV valve, intake was oily. Planning to install a catch can next time.
5. Car struggles in ramp/uphill.

When the mode switches to PWR (gas run), I get <20 mpg. Does this indicate that I should hurry to replace the CAT? I assume it's $2000+ repair with OEM unit w/ heat recycle. After market CAT from rock auto didn't seem a feasible option because of no good welding clearance and the heat recycle system.

How long can I delay on this CAT service? I don't live in CA. Any experience sharing on the cost to replace the CAT is appreciated. Thanks.

 

159k miles. I believe that the after market cat is allowed here. Thanks for the suggestion.

 

Anyone got any luck with the cleaners (pouring through fuel tank) to unclog the Cat?