Previous 20k OCI was Amsoil 0w30. decided to give PUP 5w30 a try. Only went to 10k on this OCI. I didn't feel like I could go to 20k only because it experienced a bad PCV valve failure at just over the 8k mile mark on the oil. I was expecting much worse results due to this issue. Replaced with the GM EcoTech PCV valve (built into their Valve cover and purchased from GM Parts Direct. com). It came with its own inserted gasket so I did not use any gasket sealer of any type when I replaced it. I do appreciate the kind words of Blackstone Labs for my handiwork! This report is on the Pennzoil Ultra Platinum and I did switch again and now have Valvoline 5w-30 High Mileage Full Synthetic in the crankcase. Going to go another 10k to compare wear averages against the Amsoil at 20k and the PUP at 10k and see how it compares. TBN seemed to hold its own at the 10k mark. Wear metals quite low for 10k.