I have a 2012 GMC Yukon Denali SUV, 6.2 Litre. I have a vibration mostly under torque or acceleration. if you take your foot off the gas it stops. Sounds a bit like Russ's issue - the vibration is more like going over railway tracks. I have changes U joints, ball joints, tie rods i beleive, drive shaft. Now garage thinks maybe transmission/torque converter.
Any thoughts keep paying for nothing - i have had to 2 seperate garages.