I have been running 5w30 Amsoil diesel oil now for nearly 2 years in all weather. I can't imaging it's the oil.
I'm down to 2 things.
1) it's a sensor that is not working correctly when the truck is warming in the morning during glow plugs running
2) due to glow plugs running, there isn't a correct voltage detected by the VR on the alternator (one I am not monitoring) and the truck thinks it needs to charge / not / charge / not / etc.
Next step, going to run a tap to the wire on the alternator directly to battery voltage and bypass the computer to see if there is something there BEFORE I go off and start replacing sensors.