The 6.0 common rough idle black smoke when cold
 

I have 06 6.0 I have really rough starts bad no power when cold. I did the 5-40 syn oil rev x and it really helped and kind of stopped for a couple days. Now when I start I have to cycle the key a few times and let the glow plugs a injectors buzz if I don't black smoke and sounds like I have only two cylinders. Could it be injectors or FICM? Any help would be appreciated.