ORIGINAL: Quicktime_GT

So I had FRPP 4.10 gears put in last fall by a very respectable garage, Hang em High Motorsports. Their car actually won the wildstreet class at beech bend NMRA finals.

Since I've had the gears, i've had a slight vibration come on right at 85-90 mph, It was not there before. I know there is no reason to being driving continuously at 90 mph but when I want to I dont want to feel this slight vibration. I thought it may be coming from the driveshaft, or that maybe it is suppose to only go back in one way (according to 5.0 magazine ) so I took out the 4 bolts on the yoke and turned the driveshaft at different spots test driving it inbetween every place, each still has a vibration.

What could this be? Just my junky factory driveshaft out of balance? something in the rear end?
Anyone else ever notice this?