I cannot answer that question about the knock sensor.
I think its more like a microphone and it sends out a frequency or signal that the electronics read and shift the timing to compensate for it. I suppose its powered and the sound changes something in or out?
I truly do not know how it works, just know its suppose too!

All I can say about the now clicking switch is to make sure works and most surely be plugged in!

You should be able to run any fuel at or higher octane than the one recommended in a owners manual for that year. This fuel management system self tunes all the time!

I am going with a lean mixture theory and thinking more, even though it hurts sometimes! (:)

I am wondering now if you may not have a Engine Coolant Sensor gone bad as it might throw the engine lean and off its program in the ECU? It's the one smaller than the knock sensor and farther back under the manifold. Never knew one to cause pinging....but?

Does it run with the same power as when it's not warmed up, on the flats?

Going up hills draws on the fuel pressure regulator to provide more fuel, which is vacuum controlled. It enriches the mixture by closing off the bypass back to the tank and raises up pressure in the fuel rail.
Improves power and helps keep it from going too lean.

The pinging sound is a one sized wrench, laying in a pile nuts here!

Timing change usually corrects that. The load scenario is telling us something. In old engines it was carbon but that was another era of big engines and short trips!

Check from the throttle body for a vacuum hose to a sliver can mounted to the fuel rail. Check for vacuum with the engine running. Check for cracks that might leak air in and any gasoline or smell from inside of the can or hose.

Did this come on all of a sudden? Could it be a bad tank of gas?

Again, its a empty wrench on my end.
Keep sorting!
Phil