How is your coolant level? Does it drop? It potentially has a bad head gasket, which is a known problem in high mileage gen 3 Prius cars
I have checked it .. and I have cleaned and fix problem in intake valves .. but the problem isn't solved ☹
Super low oil level will sometimes create symptoms like this... But seeing as you've done so much already to address this problem, I highly doubt you've over-looked being a couple quarts low on oil.
