Just installed my Pacesetter LT's and will be getting the rest of the exhaust welded up tomorrow. I know that running the truck without the rear o2 sensors, or without the cats will throw the SES light, since I don't have a custom tune. My question is, what is it going to do besides throwing a code? Reduced performance, gas milage, etc.? From what I've read, they just check the efficiency of the converters, correct? I just don't want to have the cats re-attached, only to remove them when I can afford a custom tune. I can live with the SES light if performance and gas milage isn't being lost. Thoughts? And no, I can't afford a custom tune right now?