Asfir sliders? This is the first time I've heard someone hear mention using their stuff. I didn't know they made sliders for the 2500/3500, but I know they make skid plates. Really, they're the only ones who provide full coverage for all the major components underneath (engine oil pan, transmission, fuel tank, DEF tank). Otherwise you're looking at adapting PW skid plates, which involves some frame modifications, as I understand it.
How do you like the Aisin? Overall, most owners seem to love that transmission, but I've heard a small, but vocal, minority complain about shifting issues (something to do with pedal lag when accelerating).
Great build so far! Thuren seems to be one of the two preferred suspension setup's for these trucks (the other being Carli).