98 S-10: Emissions - SES Lamp ON/DTC P0420 Set

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Saw this on a Technical Service Bulletin (TSB):

04-06-05-001 JAN 04 Emissions - SES Lamp ON/DTC P0420 Set

Anybody know anything about this?

This truck (2.2L) has been misfiring for most of its life, but has always passed emissions. The crossover pipe finally gave up the ghost, but shortly before, the "Service Engine Soon" light made its appearance. I had the crossover pipe replaced, light is still on. Haven't reset the PCM yet. I've been reading that bad coil packs/misfiring can cause the catalytic converter to go bad. Does this sound like what's causing my problems? (Vehicle has 130,000 miles)

Thanks!