The reason it only seems to change when you fill up is because it's an estimate. If you're driving it with a lighter foot than whomever had it previously that estimated range is going to be way off. Happened all the time in my challenger v6 when I had that because my work commute was only about 3 miles. When I'd take a trip it would say around 350 miles to a tank but then I'd drive almost 300 miles and my estimated range was still close to 200.I believe it only resets at fill up, not while driving. Some have said it will adjust while driving, but that has not been my experience.