I finally got enough time to lower my truck and get the wheels on.
-2016 CCSB 2wd, Z71, Duramax
-Belltech lowering kit. They say it won't work on a diesel, but it was basically all a perfect fit. Some minor adjustments required for height.
-KMC wheels from bbwheels/smalltowntire. 20x8.5 15mm offset. Ordered blanks from them and bbwheels had KMC drill the wheels before they shipped them so you know they are a quality drill job coming from such a big manufacturer. The guys at bbwheels were GREAT to deal with.
-Nitto 421Q tires in 265/50/20
I installed the whole kit without a hitch until I sat it down and found out my fears were founded in truth. . .the diesel having less rake than a gas truck left the front sitting 3/8" higher than the rear. The fronts were adjusted all the way down already because I didn't use any spacers. I pulled the front back apart and cut a mere 1/2 coil off the front springs and it now sits great with the front just a little lower than the rear. I used a cutoff wheel so as not to heat the spring any, so there should be no negative effects. On a gas truck it would have sat perfect with no adjustments. I did have to grind a small corner off of each rear lower brackets in the fip kit, but nothing major.
It rides great. I don't believe the lowering affected the ride at all. Going to a 20" wheel from a 17" did make some change, but not too bad.
It has not rubbed at all while driving yet. We will see after I get it aligned and drive it some more.