Join Date: Oct 2004
Location: Nibley, Utah, USA
Check tire balance front and rear, either check the motor mount torque values yourself or have a dealer do it, then trashcan the stock exhaust and mount up a Staintune. Better sound, less weight, and no more vibratoin in the 4K range--dead smooth from idle to redline. I put 22K on my '04 GT in the 12 months I've owned it, it's smoother now than it was new--to the extent that in twisties I've at times bumped up against the rev limiter without realizing I was getting close....
You shouldn't be getting any appreciable vibration and for sure should not vibration that stays with you as the RPM increase.