[Fot] high speed vibration issue

[Scott Janzen]

The GT6 had a low frequency vibration at Summit Point over  
Thanksgiving, but only flat out on the main straight (above 110 mph/ 
6000 rpm +).  It did not feel like it was isolated to any one corner,  
though I could be wrong about that.  No issues up to 7000 rpm in other  
gears.  Could this be the driveshaft, or just a mild tire out of  
balance that is only evident at high speed?