I have a 2021 Silverado 1500 LT 4 wheel drive 5.3L engine. I bought it new Dec 2020. In March 2021 @ 4500 miles the knocking and ticking started, had to have the lifters done. Then in May 2021 at 9100 the hiccuping began on the highway followed by knocking, ticking and grey smoke from the tail pipe, I had to have the lifters done again. This morning at 11,000 miles I heard a couple of knocks and the beginnings of a tick.