The start-up misfiring symptom could be the engine was flooded. After it runs for a few minutes it clears the flooded condition and then runs smoothly. A leaky fuel injector could cause that. The fluid rail is supposed to remain pressurized when you turn off the engine, and the injectors are supposed to not leak when the engine is off. Also double check the fuel pressure regulator is holding vacuum also. If its diaphragm springs a leak, that can result in a flooded engine. If this happens again remove a spark plug and see if the electrodes are wet w/fuel. If so remove all the spark plugs and let the cylinders air out for a couple days.