3.09 gear set with 3.23's

Only common denominators are the car and the engine.

Vibration is or has to be isolated to a specific rpm range if it does it on a lift, no road contact.
That would mean its the motor or bad drivetrain angle perhaps. After diff trans drivelines , rear diffs, tires, wheels, balancers n flex plates... somethings really far off in the motor and resonating into the trans... or the trans builder is making the same mistake over n over...or the entire engine and trans is offset and there is a slight kink at the tail shaft u joint.

Check if the car has been hit in the front and the k member and trans are not inline with the tailshaft/ diff yolk. You can have all the pinion angle adjustments you want..up n down.. but if its at an opposing side to side angle at one end... wahala.