The driveshaft may be out of phase. If you've checked everything else, and your tires are balanced, then you might want to remove the driveshaft and reinstall it 180 degrees opposite. Just a thought. John
'68 C-10 - 250 with Edelbrock 600cfm 4 barrel, Offy intake, Hedman headers and true duals, HEI, MSD 6A box, relocated gas tank
Soon to have: T-5 tranny
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