misfire question

[espey_16]

So my ses light blinks at higher rpms which means there's a critical misfire right??? Well when I had my dtc's read a few months ago, the only codes that came up were for my egr, and my ac (I'm not sure the code #s though). How would I go about figuring out which cylinder is misfiring??? I have somewhat new spark plugs in it, and somewhat new plug wires on it too. The wires are all good, and I have those flame proof boots on them. I plan on changing out my coil packs sometime in the next few weeks. If its not the coil packs what else should I change out???