2004 GMC Yukon Lifters in engine

This is and has been a well known problem. What you are hearing is what is commonly called piston slap. As the engine heats up the pistons expand and your sound gets lower or goes away completely. You ae fine to do nothing with the truck other than to make sure you keep the oil and oil fliter changed. You should do this evry 3-4 months regardless of the driving that you do.