[Tim john]

Here's a thought. Are the factory "cocktail shakers" in place. These were installed for a reason. Convertibles are notorious for vibration and the "vibration dampeners" (cocktail shakers) were the solution. Your symptoms are exactly why the factory installed them. Higher rpms and speeds cause the harmonics, the shakers balance/cancel them out. Your car should have two in the front and two in the trunk (one per corner).

Swap wheels front to back, side to side, etc...confirm each wheel is balanced accurately, also confirm your new driveshaft is "balanced".


Tim john---