As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
A/C PORPOISED AND VIBRATES ON CLIMB/CRUISE WITH A/P OFF. FEELS LIKE THERE IS PLAY IN CONTROL COLUMN IN PITCH. CONTROL COLUMN KICKS BACK OCCASIONALLY. REPLACED ELEVATOR POWER CONTROL UNIT, PERFORMED AUTO-PILOT AUTH CHECK, ALL INDICATIONS NORMAL.