I'm not trying to be funny or an asshole here, but are you sure it's not just in your head? The reason I say this is because last month I met up with some guys in Tennessee and one of the guys there said he was getting some strange vibrations in his driveline. I drove it and didn't feel any out of the ordinary vibes and Scott and Lane drove it too and felt nothing. You know your car better than anyone, but you might have a couple other Z guys take it for a spin for a second opinion. If you're like me, you don't spend a enough time of prolonged driving above 80MPH anyway and it could have always been there. Then again, I probably don't know what the heck I'm talking about anyway :)
Jonathan Howlett AIM-JRHZ32 1993 Ultra Red Twin Turbo 1990 Pearl Yellow Twin Turbo(Deceased)