Driving from Pearland to Houston, 20 miles one way, 60 mph, have the ECO option turned on so I keep it in the ECO mode as much as possible. Driving very light but yes, I have been getting it since I purchased the truck. The key is to not get all over it, keep the speed under 65 and all is good. Push it over 62 and you can see the mileage drop precipitously. And yes, it's getting considerably better mileage than my 2013 which didn't have the 8-speed auto thus I'm attributing it to the 8-speed and ECO.
EPA rating is 17/22 thus when I got 24.2, I recalculated to ensure I didn't screw up the math. Will keep you posted when/if it drops as I too can't believe this will last but again, a lot has to do with how they are driven. Back in the early 1980's, I had an Isuzu Pup Diesel work truck which was one of fourteen in a fleet. My truck consistently got better mileage than everyone else but again it had to do with the fact I was light on the accelerator whereas most guys were flooring them. To each their own...with my Laramie Longhorn, it's so damned comfortable I don't mind spending a little longer in the truck to get there and saving fuel to do so...
P.S. Granted, I did get stuck in traffic twice and watched the mileage go to heck but that's going to happen with any large engine. Even then, the "diesel premium" still doesn't make it worth it to me.