Loss of power

This is a bit of an odd issue that it takes so long to act up and then just restarting the engine seems to clear it up.

Here is a guide that walks through the common issues but I suspect you have a sensor issue or even just an issue with the engine oil:

https://www.2carpros.com/articles/symptoms-of-low-engine-power

When is the last oil change you have had? If you are going on this trip again or going to be driving this amount of distance again, I would suggest having an oil change done just before you leave and see if it does it again.

What makes this tough is unless you can get this to be more consistent or get it to act up in less time, it will be near impossible to figure it out.

On the other hand, if you are not taking this trip again and it doesn't act up during your normal commute then we can just deal with it when it starts to affect your regular commute. Clearly we want to try and figure this out but as I said, if you have to drive 3 1/2 hours to get it to act up, that will complicate things.

Let me know about this info and we can go from there. Thanks

I just did a little more research and I have a couple more questions. You listed the transmission as an automatic. Do you have a CVT transmission? This is the one where you don't feel the shifts. Next what was the temp outside when this happened? Lastly, were you going up and down hills before this happened?

So you are on the right path with a slipping clutch. However, you do not have a traditional transmission for the clutch to be slipping. You actually have a steel belt inside the transmission that when the fluid breaks down and the unit is hot the belt starts slipping and the PCM will actually shift the engine to limp mode to protect it from damage.

I would recommend changing the fluid out because this is called high temperature fail safe mode.

If changing the fluid doesn't solve this then the only way to fix it is replace the transmission. However, as I said before, if this only does it on long drives like this, don't worry about it until it is an issue during your normal driving.

I would still recommend changing the fluid if you have not done so recently.