Fuel pressure regulator

On the 6.0L and 8.1L engines the regulator is part of the fuel pump module, mounted in the tank. Why not have the fuel pressure tested. If the pump/regulator is bad, fuel pressure will drop very rapidly after turning the ignition off. As another test, try turning the key to one (not start) a few times before starting. This cycles the fuel pump and charges the fuel lines. If it is still hard to start, the problem is likely elsewhere.