I'll be driving down the road and all of a sudden lose all transmission function

What is your question?

If I shut the car off and let it sit for a few minutes, then start it back up I can drive it for a few miles before it does it again. Could this be the shift solenoid? or is my transmission going out? I have changed out the trans filter and did a flush. This doesn't happen all the time, it's sporadic. Thank you.