I've got a problem with vibrations at speeds over 75 mph. I have an 87 Iroc-Z 350 TPI and anytime i go over 75 the whole car seems to vibrate when it slows back down to 70. I just had the transmission rebuilt and was wondering what would make it shake like that. The front end was just worked on so everythings all set up there. Maybe the driveshaft got knicked when i took it out or the rearend has problems. i have no clue. Also, when i put the car into gear from park, it tends to jump, whether it be reverse or drive. maybe somethings just loose and causing both problems. i have no idea. any help would be greatly appreciated. thanks.