Engine Miss

 Like I posted earlier I just changed over the  exhaust to out the back and removed my side pipes.And like I said my car starts to miss it seems when the headers get warm(hot).I ordered a new set of plug wires (suppose to be high heat) and plug boot insulators.Is there anything else I should look at  for this problem.....low speed no miss....step on gas and I get a miss.Timing is not an issue had it checked after I put in the new plugs.