Rear spring question

The Charger has a 117" wheelbase so even with the GV in there the drive shaft wasn't too short. Yeah, it shortens it by about a footto 14" I can't recall exactly. I saved my stock drive shaft and just reused it when I pulled the GV out. The shaft I used with the GV was a fixed yoke on each end with a slip/spline toward the front, like in the front of a 4wd.
That is why I an unsure of where the vibration started: The angle and drive shaft were changed at the same time so it is difficult to pinpoint but I'd lean toward the drive shaft.