NHTSA Complaint #11609971 — 2018 TOYOTA RAV4

I was driving my car through the mountains on a very hot day. The speed limits are 65-70mph. After driving for a couple of hours, a warning light/message appeared: Hybrid system overheated Reduced output power The car began to have trouble maintaining speed. At one point I had to pull over and wait a while because the car became unresponsive to the accelerator. After waiting a bit, I was able to continue, but only at speeds around 40mph. I put my blinkers on because I was afraid of being hit by the other vehicles/trucks going 70. I took the car to a dealer outside of Pittsburgh and they could find nothing wrong, and no indication in the car's computer that anything had happened. I took the car to my local dealer when I got back home to Maryland, and they could find nothing. If they can't find what's wrong, they can't fix it. I have been in contact with Toyota customer service and they have no answers other than "see if it happens again". I am concerned that the car is no longer safe to drive if the temperature outside is high, and I need to go up steep hills.