While driving 65 MPH the transmission shifted out of overdrive by itself?

It could be the transmission overdrive switch has gone bad which is common. But we need to run the codes to see what comes up, you can get a code scanner from Amazon for about $20.00.

Here is a guide/video to show you how:

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Here is a scanner link:

https://amzn.to/3Qi1SS6

Also, there are fuses that need to be checked # 9 and #14 in the interior fuse panel and # 3 and #1 in the under-hood fuse panel.

Here is a guide to help you:

https://www.2carpros.com/articles/how-to-check-a-car-fuse

Here are the transmission wiring diagrams so you can see how the system works. Check out the diagrams (below). Please let us know what happens.

Okay, this code P1740 is for the TCC solenoid here is the location of the unit so you can check the connections and if okay replace the solenoid.