I recently put Pacesetter headers on my 2000 GTP and my mpg has gone down from 20 to 17. I was getting 20 with just a CAI and after I put the headers on, my mpg droped and doẹsnt run at her best.

I put in new autolight 104s with the header install and run 91 octane.

Do I need to get a tune or is something else the problem?