answer:First your gas guage. Chevrolet has always used a “floating gas guage”, They never were and never will be accurate. They float on top of the gasoline in your fuel tank. Many factors can give a false reading, one is if the float has debris on it. Go to AutoZone and get a can of Gas Dry for gasoline. Ask an attendant if you are not sure. Pour into gas tank with at least a half tank of gasoline and run the gasoline just about out. Hopefully, this will help you. Second, It appears that your engines thermostat is sticking in the closed position. Being closed does not allow your coolant to circulate and the results are no heat inside you car and an incorrect reading on your gauge. If you do not know how to replace the thermostat, then take your car to a reliable neighborhood mechanic.