Just got my latest oil report on my 6.7 I thought I would share it since I feel that getting the oil tested periodically is worth the money. Check the second attachment for the TBN on the 6.7. TBN lets you know how the oil is holding up and whether or not it should be changed. The 6.7 sample is a full synthetic at 7800 miles and Blackstone suggests another 2000 miles is OK.
I also posted the last report of my 6.4 to illustrate how these reports can be both positive and negative. Read into it as you will.