Sorry I just saw this, been on vacation for the last ten days. To answer your question, Yes, I'm very happy with the CST kit. I ran there 4" kit on my 2013 Sierra and it was a great kit. The new kit for the K2's is a bracket kit to work with all three of the different uca's that GM used on these trucks. The install is a little more involved since you need to drop the steering rack 4.5" and install a steering extension with the new kit. I did the install myself with help from a friend, took about 14 hours taking our time. Main thing is follow the instructions closely. I went with the CST coilovers in place of using my stock struts and the 4.5" spacer. I wanted the best ride possible. I also decided to do a Deaver mini-pack in the rear in place of the included 3" block.
I just got home from a Florida trip, drove the truck from Michigan to our place there, 2200 mile round trip. I got to say it was a very pleasant ride. I can honestly say the ride is an improvement over the stock ride. It just soaks up the hard jolts over bridge abutments and feels much more planted then the floaty stock ride.
I also decided to go with the Nitto Ridge Grappler in 305/55/20 C range tire, 52 Lbs. over the 10 ply same size version at 64 Lbs. to get a better ride.
You should expect to pay $800.00 - $1000.00 for a shop to install it.
Any other questions I'll be glad to answer.