The idea of turning the shaft in the end yoke would only work if the shaft was assembled using the diff and oriented that way, otherwise and which i can guarantee it is not assembled that way so it would make no difference.
That only works at the slip yoke since the shaft is atleast balanced as an assembly and the slip yoke is a part of that process, some companies assemble on fixtures and then add joints and other coupling parts and then balance the assembly, some do it with all the corresponding pieces.
When ever you change joints everything should be oriented the same, but even changing joints can put the shaft out of balance.
What Cravin described points to a shaft issue, and with the 2.9 ratio that is where it would show up
