My 2001 5.2 3.55 gears quad cab with a cap. (caps and tunnel covers help)
Would almost always get 17 (US gallons) highway AC never made a difference got as high as 18 and as low as 13 (horrible winds) depending which way the wind blew. But most always my highway average driving 62 to 72 was 17! Cruise on (and air always I love my AC) cruise on adjusting speed with buttons on right steering wheel top give 1 mph more bottom gives 1 mph less.



My 2008 5.7 hemi quad with a tunnel cover gets 18 to 20 65 mph.