Joined: Aug 2009
Location: Fort Worth
Had an issue like this on my old 08 Mustang after having new tires installed. The dealer found that the wheels were balance correctly but that the tires themselves had a "heavy side" that only showed up in like a road force test or something like that (I forget exactly) that they normally don't do for tire installs or tests unless it's requested, so they dismounted and re-mounted the tires according to the test results and the balance of the wheels and the vibration went away.
2015 Oxford White GT Manual Transmission
2013 Grabber Blue V6 Manual Transmission - Sold.
2012 Grabber Blue V6 - T-boned and totaled.
2008 Performance White V6 - SOLD!