I bought my 98 4.6 HSE about a month ago. The mileage and range figures worked fine when I got it. The first time I reset it, it showed a range of 999 and mileage of 99.9. It stays like this all the time until I get very low on gas. The range will eventually start to lower until it is around 650 when I am empty. I have reset it several times and nothing changes. Additionally, I have disconnected the battery and that didn't help. What could be causing this? Is there any connection between this and me getting very low gas mileage(10-11MPG)? It seems to run very well and I have no fault codes. Would a dealer or shop be able to give me more info on whether new O2 sensors would help? I can only go 180 or 190 miles before my gas light comes on between fill ups. Would using premium fuel help with these problems? Any advice would be greatly appreciated.