Eliminating mirrors or other things creating drag may not have a large effect on your MPG but you need to scale that up to the millions of trucks on the road. Even a 1/10 mpg improvement would result in saving a significant amount of fuel. Technology is available to replace mirrors with cameras with no loss in capability.Sure you can do things to make a truck get better mileage. But you’re going to have to give up off road and towing capability. Which is why I have a truck instead of a compact car.