"Reduced Engine Power" warning came on

Yesterday, I was driving my 2021 Lariat with PS into town. I just started it and then went down the hill from my house. I'm at 1200 ft elevation and it's about 1100ft down to the bottom. I usually downshift the transmission to 3rd gear to help control the descent and avoid riding the brakes all the way down. About halfway down the hill I got the error message in a big yellow field in the middle of the digital display, "Reduced Engine Power" or words very close to that. When I got to the bottom of the hill, and turned at the stop sign to continue on my way, I found that the engine power really was reduced--I could only go about 10MPH and it wouldn't shift out of 1st gear and limited RPM to about 1200.

There's an old joke about Microsoft Windows: "a mechanical engineer, an electrical engineer, and a computer engineer are in a car. The car stops running... " The computer engineer suggests that they all get out of the car, close the doors, then open the doors and get back in again and see if it will start. Well, that's close to reality now. So, I stopped the truck, turned it off, counted to 10, and restarted it. Everything returned to normal operation.

Have any of you experienced this? I wonder if starting cold (ambient temps were about 55 degrees) and immediately running down hill with the transmission in a low gear caused the engine computers to think there was something wrong. However, I've been doing this several times a week since I bought the truck in October, and I haven't seen this error before.

Any help appreciated.