^Except those 2 engines have never been in a HD GM truck and the Ford 6.2 I don't believe has AFM either. 6.4 Ram does, but he!!, the wife's 6.4 SRT Charger can't get 20 mpg commuting. Barely over 20 just driving the speed limit on a flat road!
And 17-18mpg in any HD is either a pipe dream, your commute is 52 mph down a straight farm road in a 2wd or you're a moving traffic hazard!
Love people's mpg claims.
Remember there's 3 things most men lie about... The size of their ____, the size of the fish they caught and the fuel mileage of their truck!
Of course we are on geezernet. A guy might be able to get 17mpg on occasion in a HD by hyper miling with the wind at your 6. The rest of the world has to get somewhere before they have another birthday, so 17mpg in a 3-4ton pickup is not happening anywhere but in someone's mind.