I accidentally bought it, thinking it was 15W-40 to use in my bike. Since I already had it, I decided to try it in my Z71's 5.3 V8. My truck got 1/2 mpg better with the Rotella T5 than the Super Tech synthetic that I'd used for years. Can anyone explain this mileage increase. BTW, the truck has almost 200,000 miles on it, and uses no oil between changes.