Okay guys here goes...just installed energy suspension tranny mount 700r4...and on the ride down to florida no problem...but on the way back...boy oh boy..about 80 mph vibration big time,,,,and the faster i went the worse it got...what gives? do i need to go back to a original gm mount? or is my drive shaft playing dirty tricks on me? any help would be appreciated..thanks.

poly mounts transfer more vibrations than rubber so more vibes are to be expected. what is strange is that you didn't notice anything on the way there. did you not hit 80 mph on the way there? did you hit something in between your trips? things shouldn't just change like that. thirdgen driveshafts are known to be out of balance and often cause high speed vibes.

you may have lost a wheel weight, does it feel like the vibration is in the steering wheel or in the seat of your pants? steering wheel feeling usually means out of balance front wheel(s).

you might check all the bolts and nuts to make sure they didnt loosen up on ya....mounts..u-joint....