9.99 CO is extremely high. We would recommend going back to basics in terms of diagnosis. Check engine compression, check fuel pressure, check for damaged fuel injector(s), ect. High CO is the result of a rich fuel mixture.
Your Chevy truck's Catalytic Converter may be damaged after running rich for a long period of time, however the CAT's failure is not causing your Chevy's high CO problem. There is an underlying fault causing the high CO, which in turn would more then likely damage the catalytic converter.
Read more about CO failures here.
