2013 Prius losing power on hills

Too much drag and resistance to go fast. Engine was revving high but gaining speed slowly. Now, THAT is NOT normal. I inspected my car.

 

It's possible there are more than one issue.

This is a serious symptom, typical of a head gasket leak causing low coolant OR a serious vacuum leak if it was egr work related. However overheating due to egr work is unlikely.

How was this resolved?

Overheating has been known to cause limp mode and may not code because of a lack of coolant at the sensors. This should be obvious with low coolant in the passenger side reservoir. A failing water pump is also possible.

A failing inverter could cause limp mode but will code and throw warning lights. The inverter related software update was intended to reduce the stress on the power electronics in the inverter before it failed.

If the inverter has failed you will get codes and warning lights. With the right codes Toyota will replace it free.

 

You may want to recheck the fill level and was Toyota ATF used? Some transmissions will run weird when you don't use OEM fluids. My brother changed the ATF on my mom's Honda and it started slipping. Changed it again with official Honda OEM ATF and the slip disappeared.

If that was the first time it was changed - Yes those plugs are jammed in there really tight from the factory. I have to use a 3-foot breaker bar; but once it's been broken loose and torqued back down to factory specifications - you should be able to unscrew it easily using a 10mm socket hex.