Try replacing the O2 sensor. It's almost always the culprit if all readings are off. I'd try the repairs myself if I was you. If it's not that it's a bad cat. Usually if it's the cat only one # is off, I forget which one. Do you know that in GA. if you spend I think its $400 in repairs, but still don't pass they'll exempt you till the next year? Keep your receipts for any parts. If you have any friends that are professional mechanics they can quote a ficticous labor to get you past the exemption amount.