Yeah I think you are right. I put the Termi slip in on mine and didn’t change much but the sound a bit. The computer is pretty smart and over time it retrains the fuel mixture based on the O2 sensor data and temp. Really don’t need a retune for one of those slip-onsThe MTS has all of the muffling & Cat handle before the "Slip-on". without the de-cat you will only change the look.