Driveshaft vibration after new gears

After installing my DMZ Long Travel rear end I had a slip joint added to the driveline and it was re-balanced. Also put in a solid carrier bearing and dropped it some. Everything was good until I re-geared to 5.29. I think the extra rotational speed exposed a new vibe. Question is, is it an angle issue or a balance issue. The vibe only occurs at 50mph and I could be going downhill in neutral (acceleration doesn't change it). My mods are a solid carrier bearing and solid motor mounts. Front of the drive shaft and the second half are nearly Parallel to each other (within half a degree). The pinion angle is 1.5 degree down from parallel with the front half of the shaft. Do I need a balance check or should I start elsewhere? Thanks

 

Did the DS get reinstalled out of phase?

Most people mark the DS do that it's assembled exactly the same way it was taken apart.

This may not apply to you with the alterations you have done.

 

I re-verified with some picture I took when I brought the shaft back from the shop. The flanges/joints all appear to be phased correctly.