i have seen as high as 600 miles to a tank in my cummins once. 23 gallon tank.
i have never seen that again.
i see an average of around 400-450 a tank right now in the cold or pushing my v plow.
thats still 19.565 when im running down the high way where my truck spends alot of time.
with the plow on all the time i will get around 17.5 or so with a 9.2 v plow.
in the summer running down the highway i will get on average 24mpg. some will call it bullshit but id call it lucky. its not un heard of to pull that kinda mileage in a 24v cummins