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Your cat and O2 sensor should be fine unless you are burning nasty gasoline.
My 1991 has 230k miles with the original Cat and O2 sensor, and still passes the treadmill smog check (but barely).
My car is oddly sensitive to its gasoline and spark plugs, and always has been. It likes Denso 'U' spark plugs and Chevron 89 gas. Make sure you have good plugs and gasoline when you go back to the test station.
Some folks swear that a fresh oil change will make a difference in tailpipe readings. I don't believe it, but I've been wrong before.
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