Make sure to double check the plug wires for any signs of burning. You should hook up the Tech2 and look at live misfire data, you could possibly pinpoint a cylinder or 2. It’s almost always plug wires burnt on mine when it starts running like crap due to the headers, and I know you have headers too.Had the o2 sensor(Denso?) swapped out. Got a little better, but pretty much doing the same thing. I think I'll pull the plugs to see what they look like, then maybe change the maf sensor. I have a spare oem. Still no cel.