B757 pilot reported an equipment malfunction during cruise affecting the airspeed indicator; autopilot; auto throttles and gear monitoring indication.

Narrative

We were at FL350 after approx 2 hours flight we started getting intermittent OVERSPEED warnings with the high speed zipper fluctuating up and down. after about 10 min OVERSPEED wearing stayed on with the zipper down to 245 knots. After another 5 min LANDING GEAR VMO/MMO advisory message came on. The auto throttles came back trying to slow the airplane to below the zipper. We had to disconnect the AT's (Autothrottles). We called Dispatch on Satcom and had them patch with maintenance. Mx (Maintenance) said there might be a switch in the E/E (Electronics and Equipment) compartment that was causing the problem. I was not going to send a crew member down in there. I discussed diversion options and Dispatch asked if we could return to ZZZ. I asked the crew and we agreed that was the best option. I was flying manual throttle. When we were given descent from FL360 to FL340 I used Level Change and the command speed dropped to 245 and the autopilot pitched up starting a climb trying to slow. I disconnected the AP (Autopilot) and we got clearance to FL 280 out of RVSM. We notified ATC we had an autopilot problem and were hand flying. Later we got a lower altitude I used Vertical Speed and AFDS (Autopilot and Flight Director System) showed proper guidance so I was able to reengage the AP. When we descended to 10000 ft and 250 kts we were below the zipper and I was able to reengage autothrottles. The approach and landing were uneventful. However the LND GEAR VMO/MMO advisory stayed on. My crew did a great job during this event. Very professional.Cause: Equipment failure.