Like pilotpip said, any Do-It-Yourself auto parts store should be able to read your trouble codes for free. That's how they know what parts you'll want to buy.
It sounds to me like a catalytic converter problem, in which case you'll probably want to find a good muffler shop. While it's possible to purchase bolt-on parts, it's often less expensive to let a muffler shop hit it with the torch.
That's just my guess -- take it to AutoZone for a more accurate assessment.
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