I have just filled my GN up with gas for the first time since buying it. The digital guage read about 4 gallons at the time and was going down. Hence, I filled the tank with premium fuel. After the fill-up, the guage read "F" (full). I have now driven the car 70 miles since and the guage is still reading "F". Is there a fuel guage sensor in the tank that reads the level of fuel? Is it normal for the "F" to remian a long time before the digital guage starts to show a lower fuel level? Is the fuel level sensor bad or should I wait to see if the guage starts to read a lower level after a few more miles? Where is the sensor located? FYI, my dash is a factory digital dash. All help would be appreciated. Thanks.