Does the engine shutdown occur when you go over a bump or as you make a turn?
I once had an '05 Freestyle that would (apparently) randomly shut the engine off completely. Turns out it was the wire from the engine pickup sensor leading to the engine control computer passing through the firewall... which was ungrommeted. The insulation on the wire wore over the years, and whenever the body flexed a certain way, the harness would move and short the pickup sensor signal (which times ALL Engine Control operations), which in turn would shut off the engine. No fault code was set to the computer when that signal disappeared. Took the Ford tech a LONG time to find the fault.
Once found, repair the insulation on the wire, put a grommet in the hole in the firewall & good to go. I offer this as a suggestion as a different place to look.
Good luck!