Took my driveshaft out to replace the seal on the back of the transmission. In a hurry I forgot to mark the driveshafts on both sides of the carrier bearing to keep them aligned when putting back together. I put them back together trying to orient the u-joints the way I thought they were. Now I feel a chatter/vibration above prolly 45 mph. I’m guessing my driveshaft is out of balance a few splines. Is there a way to re-align it or do I just rotate a spline and drive and check it over and over?

 

You likely have your U joints out of phase. Easy to miss if you don't mark them. If the yokes are not correctly lined up, you get vibrations. You'll have to pull the shaft and make sure that both yokes are correctly lined up with each other, like in this image:

 

And if you still have vibrations in correct phasing, turn the alignment 180 degrees, you may have the balancing weight on the wrong side.

 

Got it figured out, had it together out of balance. Was phasing it with the caps of the u joints correctly but guess I had the weights out of orientation. Thanks guys