Thanks again for your imput. Re: nox sensor, I am at their mercy whether it is up or downstream, didn't see report but I want it fixed and my damn truck back.
And yes, I am going to do my own rear diff service. From what I can see and readm, it looks like Valvoline full syn 75w-90 will do the trick. The vids show using the same gasket,?! not sure if that is ok or I am worried over nothing. One guy didn't even drop the cover, just sucked out old gear oil somehow. To answer the ?? of how much dealer wanted here in good ole NJ .....drum role....$650 !! Seemed crazy when he told me, yes with a straight face lol, seems even crazier now!!
OH well, onward and upward. I am learning more all the time about these trucks. Still like mine