The stock keys won't make it ride any better than the leveling keys; they are just a lever. Best bet is to see how far you can lower it with the lift keys in. You might be able to get it low enough to get your ride back without buying additional keys.
I ran that kit on my 13. Only issue I had with it was the wheel back spacing required to run it; didn't leave a lot of tire options unless you were willing to do some trimming. Loved it and I miss the ride and handling. Will do the same with the Duramax when the factory shocks go. Pics are in my gallery.
^^^What is going on with the emulsions? Where is all of the moisture coming from? I have had catch cans on DI engines before but never got anything even remotely resembling that, it looks like it is mixed with antifreeze? Everything I have ever pulled out of a catch can I have always been able to pour back in the engine. That just doesn't look normal. A good bit of the ones posted in this thread seem to be some type of emulsion.
Most of the time (not in all cases) when a dealer does a lift they sub it out to someone like 4 wheel parts or some other outfit. If the lift causes damage the GM warranty doesn't fix it. They go to the lift manufacturer or the outfit that accessorized the truck.
Have you priced them through GM yet? Last time I checked just a Ring an Pinion from the GM dealership was north of 800$ and you are going to need 2 plus the shim kits, crush sleeve, pinion seal and nut at the least. Bearings should all be good still. As far as I know no one makes an aftermarket set for 9.76".
Edit. The front you can go aftermarket for around 350; it is same as previous years.
I really don't know at this point. The spacer bolts were the 1st ones I checked when I started noticing the noise. All of that appears to be good and the noise is only on the drivers side so not sure.
They are the factory Rancho's with a spacer on top to get the 6". Been wanting to upgrade to the coilover setup so this might be an easy sell to the wife.