I bought my wife a Yukon XL with the 5.3L V-8 about 8 months ago. It's been a great vehicle and it seems almost as good as new. The 5.3L is a really smooth and powerful engine, too, but there's been a nagging problem it's had: Sometimes it idles really low and acts like it wants to die. It never dies, but it always seems like it will. Plus, it doesn't do this problem all the time, but so far I haven't been able to determine a common denominator with it. I've replaced the spark plugs, PCV, air filter, etc., and still haven't been able to figure out the problem. There are no CELs coming on either. Someone told me this seems to be a common problem with the 5.3Ls so I was hoping someone here might be able to point me in the right direction.