Engine start problems need help on a 7.3 power stroke

My 7.3 power stroke desil it has the problem when you are starting it. When you start the engine and drive it is all good. When you stop the engine and start it right up it starts right up. When you stop the engine for about half an hour or more it cranks for a long time before it starts. The glow plugs are new, so is the relay. I just changed the fuel pump and the fuel filter and it got a little bit better. I was wondering if other thing can be the fuel regulater, that is the only thing I can think of. That is the only problem. The point is soon you start the truck it will run like a mad man. If you can answer my question if that is my problem or if it is something else. Thank you for your time. Eugenesharipoff.