I switched to synthetic oil in my truck a couple of changes ago.It made more difference than I expected.My truck runs like a different truck on cold starts & runs smoother all the time. I gained 1 mpg on my last long trip. I'm running Rotella T 5w40. I'll never put dino oil in this truck again. I've run synthetic in my trucks since about 92 but this truck shows the most gains of all of them.