What can be wrong with fuel pump? If it is the fuel pump?

When I turn the key on and try to start the truck it don't start. I don't here the fuel pump running. But if I turn the key on then back off several times without trying to start it then I can here the fuel pump and then it will start. Also as I drive the truck every so often the motor will flutter like it is running out of gas for a split second. I have replaced the fuse and relay for the fuel pump and that didn't help. What can be wrong?? Thanks