Subaru Impreza 2015

Two weeks ago, on a very hot day, while driving on
the feeeway, our car lost power, all dash lights
came on so I pulled off the road, turned the car off.
The car started again no problem then a few miles
down the road, did it again. It did it several more
times, each time making it less and less between
starting it again. Had it towed to Subaru dealer
where it sat for a week. They still hadn't looked at it
so we decided to try and drive it to a different
dealer. Drove the car 100 miles to the next
dealerships with zero problems. That day was
much cooler. The dealership could find absolutely
nothing wrong with the car. I picked it up yesterday,
drove it 60 miles home. No problems at all. Today,
another hot and humid day, I drove the car 50 miles
no problem but on the return trip, it lost power
while driving and all lights came on again. I pulled
to aide of the road, turned car off, started it again
and it drove a few miles before the same thing
happened. It happened 4 more times before
coming home (25 miles). I am at a loss. What the
heck is wrong with my car???By the way, I don't
know ehat a"trim" is, so I just clicked on whatever.