I have a 2004 LLY D/A. I've been reading this forum for about six months, lots of good info. I have some general questions. Since the LLY's have both CAT and EGR systems, and many of the performace boxes increase fuel into the combusion chambers to gain HP. I understand this can cause increased smoke from the tail pipe. Doesn't that increase the carbon that can plug up the CAT and with the EGR, go back into the engine? Also, doesn't the increased fuel into the cylinders wash some of the lube from the walls? like running a gas engine to rich, and cause some scoreing of the walls over time? Has anyone here installed one of the boxes and have not removed the CAT and/or block the EGR and seen any bad results?

Since I live in CA, I hate to remove the CAT or plug the EGR, since the smog laws here are fairly strict. Other drivers can report you and send in your license number if your vehicle is smoking too much :(

Run a moderate tune then. I'd suggest the TTS Tow. It works very well on bone stock trucks, and I guarantee you will be VERY happy with the improved engine response, towing power, and better drivibility over stock. I give a A+ for stock LLY applications.

LLY VanAaken also runs very clean.