I remember years ago I failed smog. Did some testing and figured out my O2 sensor went south.Replaced it. Took it back in and failed again...my old O2 sensor was causing the engine to run real rich which in turned basically burned out the CAT. Replaced the CAT and it finally passed...and my gas mileage went up to boot.

The slight "miss" might just be the cam. I have an E.B. cam also and unless the idle is set just right(jumped and in D for my auto) mine would do the same.

I just started my truck up with seven year old gas in it and it ran like a champ...didn't drive it but it still runs like a champ lol.

Don't know if the CAT is your problem but over the years with a few vehicles I had a O2 ruin a CAT. Now I replace O2 sensors when their life expectancy is up...working or not because they always seem to go to heck within a few thousand miles of that expectancy.

Cell