You are not alone. I may be nursing same problem on my '97 and others have posted re plugged cats and their replacement, usually under 8yr/80,000 warranty.
Try a search as follows for some past posts:
catalytic cats > match any > problems > subject only > any date
98 Mystique LS v6 atx 110,000km
97 Contour LX v6 atx 125,000km
stock CD on LS, cass on LX
spoiler, tinted windows on LS only
4 wheel discs on LX only
All other available options on both
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