I have horrible vibrations over 65mph. I know that it is a driveline vibration because I can feel it in the stick. I changed the u-joints but it sis not help. A was going to get the driveshaft balanced but a friend said that it would not help. He said that I should just get a new driveshaft. What do you guys think?

1983 Camaro z28 W/ t5 tranny and a 5.0

Are you sure its driveline?Not alignment?If so, you may want to check the Tranny mount.Usually the tranny mount is broken when you get hard shifting thumps, but i have also heard that vibration over 55mph has been due to broken tranny mount.

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1987 TransAm
350 sbc
Holley 750 Vac sec
Edelbrock Performer Rpm Heads/Intake/Cam
Flowtech Ceramic Headers
Crane Roller tip Rockers/pushrods