Sorry let me start by being a little clearer. I put headers on this morning and ran it a little ran fine. The last time I got in it around 5k rpm it started missing bad. To me that sudden change makes me think it's inside the cylinder. No smoke no water in oil. Plugs and wires ok coils good. Could there be anything else besides this like egr or some sensor. Pulling my hair out on this. This is my second engine in this car if it's a piston then it will be for sale cheap!!!