I had a vibratioon at about 6K rpms in 4th gear with the stock drive shaft. After I put in the aluminum shaft in the vibration was gone. Also I did notice a differance in highway driving vibrations. Not much, but there was a differance. My stock drive shaft did have 180K miles on it though. 
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91 LX COUPE, 3.73 gears, 2 1/2 inch H-Pipe, 1 5/8 MAC long tube headers, 73 MM C&L MAF, 70 MM MAC TB, LUNATI cam,1.7 TFS Rockers, TFS Track Heat heads, TFS Track Heat intake, T5 with PRO 5.0 shifter, Griffin aluminum radiator, Fluid Damper, SSM traction bars, 190 GPH in tank fuel pump. And more to come.
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