Q: Replaced fuel pump now stalling and hard start

Depending on the reasoning for replacing the fuel pump, it may be that there are additional issues with maintaining fuel pressure such as a bad fuel pressure regulator. The fuel pressure regulator is a device which controls the pressure of fuel supplied to the fuel injectors on an engine. This works by bleeding off a portion of the fuel flow to the injectors from the fuel pump to control the fuel pressure. Fuel is pumped from the fuel tank to the fuel rail by the fuel pump. The fuel pressure regulator is normally mounted after the fuel rail to ensure that the fuel rail has priority in fuel flow. The valve in the regulator controls the amount of fuel that is bled from the fuel rail by opening an outlet port to allow fuel to flow back into the fuel tank. All injectors need a pressure difference between the inlet and the outlet of the injector to spray fuel into the combustion chamber. This is called the base pressure. If this is not happening correctly, you will experience intermittent fluctuations in starting and maintaining the engine running as you have described. I would suggest having a professional from YourMechanic come to your location to diagnose and inspect your vehicle.