Shutting off while driving......not cool

Recently, replaced the battery and the alternator. A few days later the van shut off while driving. Checked spark plugs and had the mechanic run diagnostics. He was unable to find anything. He replaced the Fuel filter.

The van ran fine for a few days and shut off while driving 20 mph. I was able to start the vehicle back up with no difficulties.

Looking for a possible solution to this.

So the engine dies but you still have all electrical things functioning? The two previous Ford's I've driven that did this needed new fuel pumps. When they failed it began intermittantly. Sometimes it would start right back up and other times it would take an hour or three.
Age/Milage of your van?

You might want to check your battery cables. I had a similar problem once where it would occasionally just decide not to start, sometimes it would shut off while breaking, accelerating or turning. The connections at the battery were fine but it stopped after replacing them, must have been a short or ground fault somewhere.

All good posts above>

You didn't mention the model year. If it's '99+ ... you can add flacky relays to the list.