I go down the highway...and hit my brakes at a stop light...my gas gauge is at 3/4 then goes all the way down to empty and the ******* light goes on...is it the sensor?

 

nah, you probable just burned 3/4 of a tank slowing down...lol... its probably the gas tank sensor - or whatever its called. this happens on lots of gm's especially luminas, once the "gas level thingy" in the tank breaks or misreads you get different readings on how much gas you have according to acceleration, deceleration and turning. now if it didnt go back up thats either your gauge, computer issue, or the "gas level thingy"

 

yeah, I'd say the sending unit in the tank, if your so inclined.here you go.