When it is cranking when not plugged in, are u seeing any smoke out of the exhaust?

Whats the temps in the mornings there. If u have some bad glow plugs, then yes if it is cold enuf, it might not start.

If you have cold temps, what weight oil u using? i know when i was using 15W40 synthetic blend, my truck had a hard time starting when unplugeed, with Synthetic, it fires right up