mileage results vary widely according to driver , road , and weather conditions
for example , a test of a 1500 Hemi......
https://www.youtube.com/watch?time_continue=13&v=I5d_Bp3gD-oanother example , Ive got an old 97 12 valve Dodge , 17 mpg is about all you will see under mixed conditions and warm weather , best it ever did was 23 @ 65 mph on a steady trip , light wind and flat terrain
more speed would drop it down pretty fast