98 LeSabre Custom Code P0420

Hi,

I am working on 98 LeSabre Custom. The check engine light is on. AutoZone retrieve a code of P0420. Both oxygen sensors have been replaced…still have a P0420. Is there anything else to check to resolve this code prior to taking the car to a muffler shop?

Also, this code appears to not affect the drivability of the car. It has been driving continuously around town for months with this code with no problem. It may need to be use to go out of town (~200 miles) before placing in shop. Is there anyone that has experienced this code, willing to give an opinion this?

Thanks in advance,

Nu_Sky

Both a sight and google search for this code/condition will reveal extensive info.