Just did my first highway run unloaded on 2015 3500 SRW aisin 3.42s . 390 miles total about 20 of those were on back roads the rest were a pretty consistent 70 mph. Hand calculated 21 mpg, EVIC indicated 22.1 mpg. My normal towing of 6000 lb trailer 20% highway 80% secondary roads I get 12.6...