Why my 1999 Honda Civic p0420 cold won't go away?

I have a 1999 Honda Civic LX with a po420 code I replace the catalytic converter about 9 months ago but I didn't replace the sensors at the time. The p0420 code came back on about 6 months after installing the catalytic converter without the new o2 sensors. Two days ago I decided to replace the catalytic converter and both o2 sensors. After driving around for a while the catalyst monitor was ready and green. I replace the catalytic converter in o2 sensors due to the po420 code and the fact that my car was also losing power during acceleration so i thought installing brand new catalytic converter and 02 sensors would kill two birds with one stone. Once I installed the Catalytic converter and sensors I cleared the code and started driving but still was losing power. Check engine light came back on for a multiple misfire so I replaced the distributor cleared the codes and i'm no longer loosing power! BUT check engine light came back on today for the P0420 CODE AGAIN. How do I get rid of this po420 code?

Possible causes
- Three way catalyst converter Bank 1
- Exhaust tube
- Intake air leaks
- Fuel injectors may be faulty
- Fuel injector leaks
- Spark plugs may be faulty
- Improper ignition timing
- Engine Control Module (ECM)

You can get a p0420 by overloading the Cat with hydrocarbons. From your story you need to turn your attention to the engine health. Check t-belt timing. Misfiring must stop. Adjust the valves on this engine. Do the plugs and wires. No oil burning. Change the PCV valve. No exhaust leaks. Save the just replaced Cat. Probably good. Also with Hondas. OEM Cats only.