What could cause my 95 Ford F150 xl 4.9L I6 to lag or try to die when you give it gas?

We have replace a Gas tank and it's fuel pump but the truck is still running rough and loosing power when you drive it. We've also replaced the injectors, I also want to know if the Fuel Pressure Regulator is causing this or if it is the timing that is off on it. Sometimes it refuses to start but it always turns over. There's no way to take off very fast because you have to ease onto the gas to be able to take off without killing it or the truck trying to die.

Replace the fuel filter. Its starving for fuel.