To recap, those who do a 4:56 gear swap seem to develop a vibration at about 70 mph. I was told this is probably due to the driveshaft turning faster and needing to be rebalanced. Today I removed the driveshaft and took it to the shop. The driveshaft was in perfect balance but, the aluminum has a "wave" in it which could be causing the vibration issue or in this case, a harmonic imbalance. I was told not to balance the shaft but to go to a place that specializes in aluminum driveshafts and have it straightened. This could cure the vibration problem but they did not know for sure.
I am seeing the 2006's are having vibration issues. I was also told that Dodge has redesigned the driveshaft so the u-joiunts can't be removed and are actually crimped into the yoke. I don't know if this might be somewhere to look on the 2006 vibration issue. I'm just going to have to live with the vibration or it would break me throwing a lot of money at my truck trying to redesign the engineering to solve the harmonic imbalance. A steel shaft is also not an option as the length of the shaft requires a thick walled steel to keep the shaft from flexing and the weight of the shaft would rob power from the engine. If you remove your Dodge shaft you will see this thing is probably about 20 lbs. Very, very light in comparison to a good heavy duty shaft.
I was also told the aluminum shaft can be tweeked very easily, even by someone overtightening the straps to hold it on a skid for shipment. The driveshaft seems to be a weak point but as far as I know, nothing can be done about it.
I'm willing to guess regular cabs do not have a vibration issue as the shaft is shorter than on the quad cab.