DEF Gauge Increasing Level

Early on in my mileage I had some weird fluctuations like that with DEF DTE (no longer have that happening anymore, and it didn't happen for very long), but did not experience the fill level amount in the display changing like you describe as far as I can recall.

I would not be too concerned over it. Just keep an eye on it. I personally add a 2.5 gallon OEM Motorcraft jug every time my DEF gauge is ~50% full. The DEF tank is 5.5 gallons capacity.

I wouldn't want to run the truck below 1/4 tank full on DEF for fear of ending up in limp mode if the truck decided not enough DEF (thus my practice of refilling to full when it reaches 1/2 full).

A case of DEF from any dealer is 2 x 2.5 gallon jugs, each jug will give you approximatly half a tank of DEF. I too experienced the fluctuations that you have discussed, could have been the system breaking in and it seems to have settled down on usage quite a bit.