I'm very sure that Coastal Flash is out of business. You'll see on the GM-Trucks forums that they haven't been returning calls, I'm not exactly sure what happened.
I've done my own cluster swap on a 2015 GMC Sierra to a 2018 Denali cluster. I did this because I added Apple CarPlay/Android Auto and by putting a newer cluster in, it adds the steering wheel control to command Siri (it runs through the cluster, believe it or not!). I did it all myself but it's not easy at all! I can tell you, WAMS is good at what they do. You'll be happy with it from them. It will be plug and play from them.
