2000 fuel pump question

When the tank gets to 1/3 full it cuts out going around corners. We took it in under warranty and they cleaned the fuel pump. It is still doing it. We can only go about 285 miles before we have to fill it up. This time when we took it back, they now claim it's all they can do. It's in the design. You go around the corner and the fuel pump thinks its out of gas. Anyone know the truth about this situation? Thanks.