I'm running into the same basic issue with the cruise, revving up to 3.5k to 4.5k. This happens most often at 60mph, and happens less often at other speeds.
When I notice it, tapping the gas peddle makes it go away.
I have no idea why tapping the gas makes it go away instead of making it worse. If the revving has anything to do with slowing the car down then tapping the gas would only create a situation where the car would need to slow down even more, but that's not the case.
The high revving isn't slowing down the speed that the car travels, it just uses more gas to go the same speed.
I called Toyota and had to talk to 3 people before someone would listen.
I'm convinced that Toyota needs to update the firmware in order to fix this issue. The question is, will they? I hope so, but I'm not betting on it.