I have been having this problem for the last few months in my 06 Mustang GT. I rarely let the gas down to a quarter tank. The first time it happened was after a fast, sharp left turn off the highway. I had a half tank of gas, but the gas gauge went to empty. I looked online and found a TSB for this problem so I brought the car in to the dealer for repair. They had the car all day and replaced both sender units. As I was halfway home, the gauge went to empty again! I turned around and went back to the dealer. They gave me a free loaner car and fixed it the next day. A few weeks later it happened again and they fixed it again. It then did it again, so I took it to another dealer, and it started doing it again! The interesting thing is when the MYCOLOR is set to blue, the gas gauge turns red when empty. I also get at computer error message displayed when the gauge goes to empty. I keep track of how many miles I have on a tank of gas, I can't trust the gauge. It does not stay on empty, it just goes up and down. It goes to empty the fuller the tank is.
Does anybody have a similar problem? I love everything else about the car.