Prius loses power while driving.

"Your mechanic" doesn't have to correct tools then. A copy of Techstream would be the official way of doing it, but a $10 bluetooth adapter and a phone work just as well. You need to read the codes. When the lights go off, the codes are stored historically.

Most probable causes for lack of power that fixes itself is inverter overheating. This problem is commonly caused by a failed or blocked or empty inverter coolant pump. It could be anything and without codes it's all guessing. But that's where I would start.

Open the hood with the car in READY and check for fluid movement in the inverter coolant reservoir.

 

You probably have a failed inverter pump. That's been a common failure on these cars after 100k miles

 

My prius does the exact same thing. Have taken it to 5 mechanics and none have been able to help me. Just as I am ready to give up and buy another vehicle, the red triangle, the (!), and the VSC lights turn off and it drives fine. Should I give up on this car?

 

Follow the advice the OP didn't. Read the codes and check for coolant movement.

 

I saw that advice some time ago and I checked the pump for movement. There was movement and I also told the mechanics to check the inverter pump, but they always responded that the car was fine.

I sought out hybrid mechanics who said that they could read the codes and even my local Toyota dealership failed to solve the problem.

 

have you checked your 12v battery? Have you checked your engine oil level?