Everything else looked good, but here's the important part of the analysis:

>>>>TBN 7 starts at 12 so your engine is
depleting this, like nitration needs to be monitored.

If there is an engine problem, such as EGR, which causes increase in nitration, the TBN will drop and the oil will thicken

>>>>Vis 12.6 thickened to 40w barely,limit
is 12.5 for 30 w. Amsoil is not holding up, I can't see extended drains
with this oil.

Sure looks like there is a mechanical problem, although maybe not super severe.
As I understand it, an oil can go out of grade by one step and still be usuable. The difference between 12.5 and 12.6 is pretty minor, though it is a grade on the scale.


Would be interesting to see what Mobil 1 would do in this same engine under the same circumstances.