What was found
AT FL350 AFTER APPROXIMATELY 2 HOUR STARRED RECEIVING INTERMITTENT OVERSPEED WARNING AND THE UPPER ZIPPER KEPT MOVING UP AND DOWN. THEN AFTER 10 MIN OVERSPEED WARNING STAYED ON AND ZIPPER WENT TO 240 IT S AND STAYED ON. THEN THE OVERSPEED GEAR VMO/MMO ADVISORY MESSAGE CAME ON. HAD TO DISCONNECT AUTO THROTTLES HAD TO BE DISCONNECTED. POWER KEPT COMING BACK TO REDUCE SPEED TO 240 ITS. ON ARRIVAL WHEN I ATTEMPTED LVL CHANGE AIRPLANE PITCHED UP AND TRIED TO SLOW. HAD TO DISCONNECT AUTOPILOT AND HAND FLY DOWN TO LOWER ALTITUDE. ONCE BELOW 250 KTS EVERYTHING WORKED, HOWEVER GEAR VMO/MMO ADVISORY MESSAGE STAYED ON TILL LANDING. IAW AMM 31-51-00-5 VMO SWITCH FOUND IN DETENT. SWITCH WAS RETURNED TO NORMAL. ACFT OK TO CONTINUE.