Chevrolet: 2001 Cavalier Fuel Issues, fuel issues, fuel line

Question
I have a 2.2L 2001 Cavalier, and the car will not start when it gets around 1/2 tank.  I have already changed the sending unit in the tank, but it is still doing it.  I put more gas in it and it starts.  I know it still has plenty of gas in it.  Is there anything regarding the fuel pump that can cause this?  I'm thinking maybe a check valve in the pump?  Can the check valve be replaced?  Could it be a fuel vent?  I don't know I'm stumped...Please help.

Answer
HI FRANK;
        I WONDER IF THE FUEL LINE COULD HAVE ANY DIRT IN IT, . HAVE YOU HAD THE FUEL LINE SERVICED SUCH AS FLUSHED OUT AND FILTER SERVICED.
YOU SAID THE FLOAT IS OK IN THE TANK AS IT IS NOT OUT OF GAS RIGHT.IT COULD BE THE FUEL PICK UP TUBE I WONDER IF IT IS TOO HIGH IN THE TANK? WAS THAT CHECKED ...?

PS  Get back to me if you still have trouble , I wonder if the gauge is faulty and when you are out and add more it will run again do you think that the gauge might be bad ?