Please help solve my puzzle!

[JMBT]

I will be sure and check that. I noticed on the last forced regen (yesterday) that the inlet NOX was reading higher then the outlet. I thought it seemed odd, but then when the SCR catalyst temp cooled down after the regen it went back to normal, (Inlet high and outlet low). Both readings reported "stable" the whole time, so when it went back to normal I thought it was a product of the heating up of the catalyst. My engine's NOX sensor replacement history: inlet replaced 2 times and outlet replaced once, but the check engine light came on each time.
Very interesting info on the driving regens being based on time, and 36hrs makes since. When my truck was brand new the longest I would get between driving regens was about 1800 miles, which would be 36hrs at a 50mph average. Very interesting. Thanks again for the info.
I am waiting on parts for the exhaust leak, should be in tomorrow.