gas gauge
 

my gmc sierra and my wife yukon gas gage will show empty when the tank is way above empty why is that both are 2001 veichels

gas gauge on my 2001 sierra and my 2001 yukon sticks can be half full or even full but gauge will show empty, why is that?

Usually it's the float on the sending unit sticking. However, some newer vehicles use a full electronic display rather than mechanical on the dash. It's odd that both your vehicles are doing it and the same year model. If I had to guess I'd say aliens have invaded your neighborhood and the magnetic field of their cloaking device is causing issues. Call the Air Force and advise.

The gas senders in the similar year vehicles to yours are just terrible. There's a float and a variable resistor in the tank that shows full or empty. Personally, it costs too much to fix the issue, so get some backup gasoline and drive around with it for a while. Fill up your tank, reset your trip meter and drive it until it starts to sputter. Then just drive within your mile range according to your trip meter/odometer.

Either that or go get a new fuel pump for both vehicles.