I don't think many of them are that accurate on the estimate till you begin to get near 1/4 tank and then the accuracy goes up. Just about every time I full up the 2018 Denali 6.2 liter, the estimated range is around 555-565. By the time it nears 1/4 tank, about 6.5 gallons, it begins to be relatively accurate. EPA estimates are 14/22/17 mpg but our combined mpg is 19.12. When the low fuel light finally lights up, I can put 23 gallons in it, about 60 miles worth of fuel, which is very close. That's about all the accuracy I expect from those systems that are built into the electronics of the vehicle. 522 miles is our top distance per tank since we have had the vehicle and that was about 90% highway cruising at 70-75 mph. I might add that my wife has put probably 90% of the mileage on the truck and she is a gentle driver.