I always find this discussion interesting. I must say I watch the instant MPG, when it's not on cruise control, I use it about half the time. I do know that not using cruise control does imporve my mileage a "little". I have a 2013 Knight 40df, 9.3L 350HP International, weighs approx 33,000lbs, I've yet to weigh it when it's loader, fuel, water, etc. I tow a Tahoe, 5500 lbs. I just did a 5500 mile trip from panhandle Fl to St Mary Montana and back. Everything went and worked great. Loved it. Lots of mountaines, I usually cruise at 62-65MPH. Tach reads 1500RPM at 65MPH, sweet spot is 1300-1400RPMs. Mileage was ranging between fill-ups from 7+ to 8.7+, never averaged less than 7+MPG between fill ups. So far I'm very happy with the performance. I hate to say it, but when I'm not towing and AC is off, on flat country, I have gotten 10MPG on the highway, no kidding. AC seems to reduce by maybe 0.5MPG and towing the 5,500, seems to be 0.5-1MPG depending on the roads and mountains. Mostly it's about the mountains, 7 in mountains and 8+ otherwise, towing with the AC on.