I have the same problem with my 2000 GMC Sierra with 5.3/auto. Mine only does it when it is cold though. Took it to the dealer a few years ago and they just told me to live with it because they know I wouldn't want to pay for the diagnostic charges. They did not find any service bulletins either. Just one of the many, many complains I have about this truck...should have kept my K5 Blazer. If it makes you feel any better, the condition has not gotten any worse since I noticed it a few years ago. Should be nice enough soon so that I can drive the Nova daily and forget about the truck for a few months.