Worse case, you got bad hg or head it's leaking into the cylinder over night smokes when you start it. Engine get hot it seals up while driving.... That being said we all think of the worse case when it comes to the 6.0,
Water in the oil?
Fuel in the water (your degas would be foamy)
Leaking hoses or degas bottle?
Leaking water pump?
Leaking heater core?
I would def. start with the small stuff
How long has it been since you did your egr/oil cooler
Have you been running your heater?
System could have just purged all the air out the heater core is the high point and can hold air for a while.
It could be all kinds of things I would start with checking visually for leaks in the morning after the truck has cooled down over night. A little white smoke may be just condensation from sitting over night.
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