I have 3.23 on mine and I believe the 2019 V8 is more efficient with the DFM. I don't use the cruise control, I maintain a steady foot on the gas pedal so that the DFM doesn't keep turning on and off. I never use the cruise control, I just wish there was a 30-mph leeway with the cruise control, ranging from 50 to 80 mph, depending on terrain. I hate braking while going downhill and I hate flooring the gas while going uphill. I'm OK with 50 mph to 80 mph, it doesn't have to be exactly 65 mph.
EPA highway gas mileage on mine is 20, I believe, it's a 4x4. I think EPA's testing method includes a full throttle a few times even at highway speeds to stimulate merging into traffic. I don't do that.
Some cars are immune to my hypermiling techniques. I could barely hit the 26 mpg my Benz C300's EPA numbers showed, even going 60 mph for a couple hours. It sucked! My Isuzu Trooper said 19, I was lucky to get 13 mpg! No DIC in the Trooper, all hand-checked.
My 2012 Ford F-150 responded very well to my hypermiling techniques, usually got 3 to 4 mpg better at 21 mpg, but the 2016 F-150 was pretty much in line with EPA numbers, I was lucky to get 18 mpg in a mix while EPA numbers showed 15/19. Both were Supercrew 4x4 XLT's with 5.0 V8.
EPA no longer does the flawed technique which resulted in Prius getting way overly optimistic numbers. I don't know what part was changed though.
I have my car in metric so it measures how many litres for every 100 kilometers. When I'm coasting, I do see zero which would be accurate. Zero litres consumed per 100 kilometres. I don't know why it would not show above 99 mpg which is obviously not accurate.