You NEED a tuner and that's all there is to it. The PCM monitors exhaust back pressure (fore and aft) and temperature. It needs to see readings from these sensors in its expected range.
Your tuner removes these strategies from its operating parameters. If you can still find an H&S then it comes highly recommended. These days we are sourcing tuners from SCT.
edit: also, the mileage gain is excellent. I went from about 22 litres/100 km to 16. And no building oil : )
2003 GMC Sierra 3500 -- dually, 4x4, hasn't blown up yet and that's what i look for in a truck
Ford Doctor -- They come in broken and leave fixed. Ford of Canada Master Tech