My fuel pump keeps shutting down while driving the car. once it shuts down the car will not start sometime for a few days then will start a drive for a little bit and repeat. I have replaced the fuel pump,oil pressure gauge sensor,camshaft sensor,crankshaft sensor,erg valve,coil pack,spark plugs,fuel pump relay,ignition module computer,water pump,intake manifold gasket, fuel filter and have cleaned the gas tank with using new gas. When the car is running it runs good but when you get to about 50 or so you can feel a sputter like it's not getting gas. Could this be the fuel pressure sending unit? If not what else could be the problem?