Oh my god!!!! I've got the entire dash tore apart and it's still there. I think I may have the same issue you are having with the egr being cracked.... could you see the Crack while it was still mounted on the truck?
My 2018 Denali is doing the same thing and I've tried turbo heatshield, egr heatshield, visor screws that needed to be tightened... I can't figure out what's vibrating on the passenger side dash behind the upper glove box...