when my car has a quarter of a tank of gas left or so. My gas gauge goes from half a tank to empty, back and forth while driving. is all thirdgen like this or is just my sending unit going bad

Could be or you could be missing the baffles in the tank.

The gas gauge reading is a common complaint in our cars, so you may have to do further research to ID any real problems.

JamesC

would the 4th gen gas tank make the fuel level sender a more stablized reading