current cruse control matains a set speed, when accending a hill or rise such as at an overpass, the mpg drops a lot to matain that selected speed. With the, lets say accelerator set for a given amount of fuel supply to matain a set speed with out automatically adjusting for grade, then the mpg loss is much less, even though speed will be reduced just a little, the accelerator control would need to limit the extra speed gained when decending the grade.