I just installed 3.73 gears (had my diff rebuilt by a highly recommended shop), Unitrax half shafts, and replaced the u-joints on my drive shaft. driving the car yesterday I thought I felt a very slight vibration around 80 to 85 mph. I shifted from 6th to 5th and it didn't seem to change, which makes me think it is behind the trans. It didn't get worse with increasing speed (accelerated to approximately 100 mph). I know the half shafts come balanced, so I think that eliminates them. I checked all the bolts and everything is seated well (u-joints seated in the yokes) and snug. I am considering unbolting the drive shaft and rotating it 180 degrees on the pinion yoke. should I be worried about this? should I have the drive shaft balanced? I'm going to drive the car again and make sure it really is a vibration and not just the car (hadn't driven it for a few weeks).