I have a 2006 Nissan Sentra and no matter what gas station I go to, the gauge never moves past 3/4. What could be stopping it from filling all the way up?
Your float in gas tank has either got something stuck in it keeping it from going on to full tank, or it's got a dead spot and your sensor's not reading. More than likely your vehicle hit a pothole and that bent the dial just enough to keep it from going to top.
To fix it, you'll have to pull the float out of the tank. Make sure when you raise float around all way up the little ATM on side goes to top too. That's what reads how much gas in tank: float arm goes up, little arm on side runs up and down the sensor for reading gas measurement. The other fix would be to replace the float in the tank. Good luck!
(Alternately, you can sometimes fill the tank up as much as it can go, then hit a little pothole or speedbump. If it's just stuck, that may jar it loose -- I've done it.)