Got mine back after a list of items the dealer did, most of which was alongside the local GM Field Engineer.
None of the replacement parts helped the vibration (tires, shocks, axle, more tires, RF balance, etc) however, they finally indexed the tires after one of the RF balances, and found that a couple tires were indeed slipping on the rim. From what I was told, as much as 5"-6"...
So this morning was the first time I was on the highway and it did feel better. Not 100%, but definitely better. So when I got to work, I went ahead and marked the rim to the tires, just to test the theory. Well, this afternoon on my way home, although not as bad as previous, it was definitely worse than this morning.
Well, checked my marks when I got home and the left rear tire had moved about 2"-3" on the rim. The right rear was about a 1/4" off. With around 4 oz of weight, I'm sure this would have an affect.
The real question though is why??? Why are the tires slipping on the wheels so bad? Mine even sat overnight prior to them doing a final test ride also.
BTW, my pico readings went from 30 milli-G's down to 18, which according to my report was within spec.
Guess I'll be back next week to the dealer... Starting to really miss my EcoBoost...