Still using the tripmeter.
Hmm, this DIY fix exactly that....
It is not that you can never fill your tank, it's rather your gauge is display incorrect level in tank. Your gas gauge show empty while there still gas in tank; therefore, when you fill it up it can only takes 16 - 17 gallons. You may also notice that the gas gauge will not show full even when you fill the tank. Which part of Chicago are you coming from?