2020 Ram here, just turned 1200 miles and a nice road trip to break her in...comparing it to my 2018, I can't fill up more than 22 gallons when almost all the way empty. Took me some slow filling today to get to the 394 mils to empty mark. I did a lot of highway driving, so I was hoping the computer would "report close to the 420+ range". As my 2018 would be giving me those numbers in a similar road trip scenario.
As some people reported, once filled up all the way, my 2018 would take quite a bit of driving before the fuel needle would start going down. This one starts showing gas usage almost instantly on the gas gauge. Makes me believe there is something in the gas tank system that does not allow it to be fully filled up. 22 mpg is my advertised highway mpg (on the window sticker w e torque, and I'm sure this is @55mph factory testing "going downhill", no head wind, not load on the truck and probably 4x2) and a 26 gal tank should yield close to 500 miles. I can't even break the 400 mile mark! She will probably start turning better mpg soon, as the ride is phenomenal, quite an improvement over the gen 4, and that one was great! So far I love the truck and the way it handles. I got a bunch of compliments from my Ford die hard buddy after he took her for a spin...