I have a 99 Silverado w/5.3L engine. The idle speed is too low. It gets as low as 430 rpm when I firsty put the tranny in drive and then the idle increases to a more acceptable level. There are no DTC's. This problem is most noticeable when you pull up to a stop. The engine rpm's get low enough to dim the lights and almoist stall the engine. The engine has 62k miles.