I have a high mileage 2002 Buick Century. My gas gauge is acting very weird in how it reports fuel level. I know it is common for a fuel level to vary when you are parked on an incline. However, mine is out of control. I can be below E, with a warning light on in my slightly pitched driveway, and be a half tank or better when I start to drive up the road (which is a slight incline). At times, I have seen the level show a variance of E to F, depending on the incline. As I mentioned, this is an old car with a lot of miles on it, so I am not looking to spend a lot of money here. Any ideas?