I have medium to heavy acceleration vibration that occurs @ 20 mph which goes away once the trans shifts into third gear and what feels like out of balance tires/wheels @ 70 mph. It's been in 5 times up to this point without a resolution but the dealer who has very good up to this point will be replacing a major component.
Mine is in right now for this reason, 2014 Z71, 3.42 rear. I'll let them figure it out but I found in the many posts about this that GM is attempting many things to try to resolve this.