I put my new 2024 GMC Sierra 3.0 Duramax to the test to see how driving just 10 MPH over the speed limit impacts fuel efficiency. I ran the same 85-mile loop around Phoenix at two different speeds: 65 MPH and 75 MPH. The results were absolutely mind-blowing! At 65 MPH, my Sierra achieved an impressive 33 MPG, but at 75 MPH, it dropped to just 23 MPG. These results show just how much speed can affect diesel fuel economy. Join me as I break down the numbers and share my astonishment at these shocking results. Whether you’re a diesel enthusiast or just curious about fuel efficiency, you won’t want to miss this!