I have a 97 trans am with the spec clutch that i have had for about 20,000 miles. i have a real bad vibration at about 4000 rpms with the clutch in or out going down the freeway. It is real bad in first and second butit does it through all the gears. the funny thing is that it is not all the time. You can also hear and feel it when going about 35 and act as if you are going to put it back in first or second gear with the clutch pedal in but you do not put it in gear just hold the shifter to where it is fixing to go in. I think it may be bearing in the trans or maybe the disk is not laying completely flat against the flywheel. Any suggestions will help.