Pinion Angle/Tailshaft Bushing

Assuming no tire changes,and no ride height changes,with the new gears, only one thing changed; the power train speed,at any given mph. That is from crank to pinion gear.
If you previously had 3.23s you are now at about a 21% higher rpm for any given mph. ( the Speedo was corrected, yes?). So the vibration, if pre-existing, should have been there at a 21% higher speed, with the old 3.23s. This maths out to about 67 mph, previously, as compared to 55mph, now.
If you did not have an issue at that earlier mph, then I would have to ascribe the issue directly to the chunk, or that the new rpm is exciting the natural body oscillation.