If you've ever let it get really low, does it read the same amount under "E" that it does under "F"? (don't forget, GM typically put some "reserve" into the gauge reading)
If someones monkeyed with the gauge, or the gauge itself is just "off" it can do that too.
Mine never goes quite to "F", but I've never let it get so far down to tell where "E" really is.