Dropmember driveline vibration blues

[JNJchev77]

Specs-
'77 c10
dropmembered front and rear (4-link)
5.3 w/ 4l60e.
Double cardan joint at trans. Trans angle 5* down (recommended for dm setup)
Pinion 2* up (recommended for dm set up)

I have a vibration at about 65mph+, feels like it towards the front of the driveline. Also on deceleration I get a pulsing vibration in the rear.

I'm not really sure where to start. I replaced the rear ujoint and nothing changed. I've also adjusted my pinion angle to see if any position gets better or worse... no noticeable change.

At this point I'm ready to take it to a driveline shop and have them look at it but thought I'd check in here first. Any ideas guys?

Justin