Hello everyone, here's the history of the current problem. Bought a used 2003 Subaru Legacy with 190K miles. after 1 month P0420 cat efficiency code tripped the engine light. The light seems to come and go with no repair work done. 2 months later the car hesitates severely upon acceleration but does finally get going. I am not limited to any certain speed on the highway yet. Exhaust shop said cats were fine after they cut a hole and actually visualized the inside of the cat. Then I took it to firestone who said it WAS the CC. There was no diagnostic work done as admitted by firestone once they say that the P0420 code had been stored in the "computer". Was quoted 1200 to replace CC and 1100 to replace the O2 sensors. Should I believe the exhaust shop or Firestone? Can I replace the CC myself?