I have an 08 Silverado 5.3L w/ about 23k on it. My truck idles around 500 rpm, but will occasionally drop a little and have a little bit of a shuddler/shake (not to where the truck shakes, I can just feel it in my seat). When I say drop a little, I mean just below the 500 rpm mark. Then it will go back to normal, or maybe a little over the mark. I notice it does it more when the AC is on, but sometimes without. For you guys with an NNBS, what does your truck idle at and does it do what mine does? I thought I read on here that somebody with an 09 had a throttle position sensor that was bad, but mine doesn't do it anywhere near what his did. Could I have a bad sensor or should I just run some cleaner through it or Seafoam it and see if that helps?