I also have a 2021 1500 with the 5.3 engine. It is a month old with 2300 mile on it. I had a engine knock the other day and the truck had to be towed to the dealer. They are telling be it is a stuck valve and that they have to replace all the valves and that they have several other trucks with the same problem and that there is a bulletin on it that 90% of the truck are going to have this problem. As a result there is no parts available and they have no idea how long the truck will be down.