Robin,,In your rear run box one of the boards is the start run board, it has the switches on it so you can start from the back, my coach would just shut off for no reason Cat dumped the ecm no codes. The next time it dies don't turn off the key just stop if you can go to the rear open the run box and see if all the little led's are lite, if not on push and wiggle the board and see if everything lights up. If that board fails nothing in the box will light up. My board had a short in it somewhere, got a new board from Northwest Rv supply.
Mine would shut off going down the road, finally got bad enough that I figured out the problem.