why does my fuel gauge bounce

well,that would be the sender in the fuel tank.float/switch is bad.BAD to go out on the chevy's.you have to replace the entire fuel pump module assembly,as the sending unit is part of it.thats all that float is for,to let you know how much fuel is in the tank.you can replace it by removing the bed,if it's not a crew cab,cause the pump is under the back seat on the crew.if regular cab or extended cab,remove the bed,fuel pump will be looking at you.or you can set your trip button on the odometer and keep up with the miles.if you get 400 miles to the tank,fill it up and, when you put 300 on it,fill it back up and reset the trip button,your pump is still working.