I have a 2000 chevy silverado 5.3 with 230k miles. When its in park it idles fine but when in gear like your about to take off or at a red light it idles real rough sounds like its about to die. It doesn't do it all the time but most of the time it does and when your driving down the road it runs perfect. I have replaced the fuel filter,air filter also changed the spark plugs, wires and have cleaned the throttle body. Has anyone had this problem or know what the problem could be? Any help would be appreciated thanks.