Fuel gauge doesn't read correctly when fuel gets to 1/4 left. It'll drop all the way down to empty even know it has fuel.

Mines actually a 19 gallon tank, and its normally like 12 gallons to fill back up

Professional grade scanner is capable of testing fuel % in tank so it can be compared to gauge reading .. It's very possible the 'gauge' is the culprit.

I also have a tracker on my car and it gives e the fuel levels. Its connect threw the diagnostic port. It'll read the fuel levels but won't read the same as the gas gauge

Well then that should be a clue! .. However since you 'can' keep track of fuel level, why worry?