I'm having a vibration issue as well in my 14 rcsb sierra 4.3.. 2wd sle
It comes and goes, but seems to be more often when I'm in 4cyl mode..
There are soo many pages in this thread, and I didn't read them..I know I should but I honestly don't have time but I did skim through.
Is there an answer? Driveshaft? Tranny? Engine unbalanced when it goes to 4cyl mode...
Thank you
Joshua