As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON CLIMB OUT, LEFT PROPELLER RPM DROPPED FROM 2200 TO 1900 RPM. PILOT TOOK NOTE AND CALLED IN FOR RETURN. MAINTENANCE HAS NOT DETERMINED THE CAUSE AT THIS POINT, TROUBLE SHOOTING IS CURRENTLY IN PROGRESS, SUSPECTING EITHER PROP GOV OR OVERSPEED GOV.