My '99 Silverado never did it. I sold it to my secretary, whose husband put another 200k on it. Still doesn't do it. My Dad's 4.8 did it, though, and still does it at 120k or so. My cousin owns it now. I've also got a buddy with a 2004 Suburban 5.3 and he's got over 300k and his has never done it, so I'd say it is safe to say they don't all do that.
My Dad was a GM engineer and was told by Chevrolet engineers that it was carbon build up in the upper cylinder. They did a carbon removal treatment at the dealer and it disappeared for about 10k miles and then returned. They said they could keep doing it, but it would always return, but it would not affect reliability or long-term durability, which turned out to be the case, so he never bothered with it. Not sure that's what it is, but the evidence suggests at least for his 4.8, that was the issue.
