https://youtu.be/v8SNMebcb5Q Apologies if this has been posted. I thought this was kinda cool. This man is self-employed, towing RVs across the continent for a living. He's got just over 1 million miles on his 2006 and just over 500k miles and counting on his newer GMC rig. Of course, the question we all want to ask is "What lubes did you use?" But I don't think he ever mentions it - he does, however, mention his OCI is 10,000 miles. Based on member DNewton3's experience with the Duramax engine, I wouldn't be surprised if he was using dealership bulk. At about 11:20 into the video, he starts to talk about his maintenance schedule. His biggest takeaway - "Read the owner's manual".