So driving my 97 cobra 5 speed any time I go above 65 mph on highway and I don't press the gas break or clutch my car seems to vibrate, and if I go any faster my car will vibrate worse, I just got balanced tired, car drives straight as an arrow with no wheel vibration.. I'm assuming it might possibly be the driveshaft of even worse the rear end, any suggestions

 

Where do you feel the vibration at your hands or your seat

 

Drop the driveshaft and check the u-joints. Also check the shaft for any bends in it. Sounds like its speed sensitive. Get her up to about 80, take it out of gear and see if it shakes the whole way down until 65. And just because the tires are balanced out doesn't mean that one is not out of round.