Been running great for about a thousand miles but just started hearing a random pop (backfire?) from the exhaust. Have a misfire code on cylinder 8 but plug and wire looks good. No power loss or engine cut back. Could it be a cat going bad? Only happens at idle when hot.

 

If it's only #8, its most likely specific to #8 - plug, injector, contact in Opti cap, corrosion on wire in Opti end, bad valve, etc.

Do you have access to a scanner with "GM Enhanced Parameters", that will allow you to check the misfire count on all cylinders, to see if it really is specific to #8?