I own a 2003 Ext. cab Z71 with 130,000 miles. Only when the climate control system is on it idles rough and the lights, inside and out, slightly dim and go back and forth to normal. Like I said this is only when I'm running the a/c, heat, defrost etc. I recently had the plugs and wires changed as well as the fuel filter. Another problem I have, and this may or may not be related, whenever the heat or A/C is running a noise occurs about once every 5 minutes or so that sounds like a clunking coming from behind the dash. It sounds like the fan is catching on something or hitting something. It does not affect the performance of the a/c or heat at all. Whenever the defrost only is running it doesn't do this. Thanks for your help..