I know this has probably been beat to death but I'm confused about something. So I was running castrol edge 5w30 or another name brand full synthetic and I decided to get an oil change a couple thousand before the actual due date as winter is approaching. The oil still had life left and my truck olm never said anything. I got a fresh oil change with the Dexos 2 gm stuff at the dealership and wow the truck sounds and drives way smoother and better now. It just feels completely different at the same oul weight. What I don't understand tho is that the old oil that was in the vehicle before was full synthetic name brand and still had tons of life left but now with fresh oil my truck sounds and drives way better? Anyone can explain this? Cuz I know for sure the old oil in the truck wasn't bad and easily could have been run longer so the answer can't be "the old oil needed to be changed"