I deal a bit with instrumentation. If your temp sensor or gauge is going bad, I would be extremely surprised if that resulted in a false high reading. If it's going bad I'd expect the reading to either be all over the map, or it would read nothing at all.
Take it out for a drive, once it starts reading high pull over, pop the hood and take ir temp readings to find the source.
I believe the same thing in regards to the instrumentation and in regards to the 2nd part - I did, hence where the readings came from that I posted above.
