Hand calculated, every single gallon since I bought it, I get 7 MPG on my 2015 Anthem, including all Aqua-Hot & Generator usage. I get 8-8.5 when driving. I have gotten 1100 miles on one tank... once. But I got 137 gallons in the tank... I was running on fuel vapor and took it easy and had a 1000 mile tailwind and didn't stop.
I am completely satisfied with range on the 150 gal tank. I would also prefer 200 gallons for a better ability to 'tanker' cheaper diesel when found.
If I'm towing heavy, which I definitely have done, I've gotten as low as 6 MPG. But that's hauling 25,000lbs uphill, against the wind, WOT the whole time.
I have to really say, I'm completely thrilled and satisfied with the 450HP Cummins. It's not a race RV, but it'll go 95 MPH downhill and I'll tell you one thing.... that's fast enough for me!