Mu egr cooler was leaking into the intake manifold, got ecu flashed from green diesel engineering, block off kit from sasquatch parts, and bye bye egr cooler, now my coolant stays full
Here's a potential final update. Around Friday 8/23, the dealership called and said the truck was ready, however I would not be able to pick it up until the following Saturday.
Now for the meat and potatoes of the diag (paraphrasing since I don't have the sheet in front of me):
Tech states after coolant pressure test revealed no leaks in radiator or oil cooler, an extended diag and tear down was ordered. This revealed a failure in the head gasket around the left-hand cylinders. This also caused a failure in the main bearing. Ordered engine replacement and turbo coolant lines. Installed engine with "new assembly fuel injectors." While performing the road test after replacing the engine, the tech encountered a new code P26AB, 3-way coolant valve. However, this ended up being a connector wire that pulled loose around the drivers side front wheel well. Once this was repaired (the dealership covered it so I suspect someone forgot to disconnect something when taking the cab off), the code disappeared.
I picked the truck up last Saturday, and had it for about a week and have not noticed a drop in coolant. (Just a hair above the seam when cold) Nor have I encountered any new codes after ~200 miles. So this appears to be repaired finally. I also got a SofaKing tune for the truck and I am very happy with the results (mainly the elimination of lag when throttling).
So if you have come here from a search encountering the P04DB crankcase breather code, hopefully your solution won't be as involved as mine.