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The same exact thing just happend to me this last weekend. The week before the CEL came on on the Tahoe so I went to o'reilly's and borroed there Scanner and it showed the P0420 and P0430 codes which are Catalyst efficency belwo threshold. I figured it would not be that big of a deal to drive it for a couple weeks till i could get it figured out. Well i attempted to accelerate up a hill and the truck lost power the RPMs started to bounce and the CEL started flashing. I took it right back to O'reilly's and it showed a code saying there was a missfire. I have read that a clogged Cat could definetly cause a problem within the Cylinders and a missfire because the gas has not where to escape.
Diggerdan you definitely need new converters.