OK, so you need a scantool of some sort to check for CPS function (earlier trucks move the Tach while cranking to show it's working). And a truck that dies on the road and then restarts once "cooled-off" often is about a bad CPS (be sure you ONLY use a Ford/IH CPS).
If you're gonna keep & maintain the truck yourself I strongly suggest you get access to the special scanner software you need to do it.
Here you have a couple of the most common choices;
1) If you want to do Everything you'll ever need to, then look at the AutoEnginuity + the Ford Enhanced Package (@ $350 - you add an old computer of some sort to run it with)
2) To retrieve most of the codes you'll need to help and even do some
testing look at the FORscan Lite or TorqueApp (you add an Android device and Blue Tooth Adapter for @ $30) OR the Windoze version with a USB adapter. I like this one for BT Android -> http://www.amazon.com/BAFX-Products-...dp/B005NLQAHS/
Just a few years ago you needed to buy a professional scan tool because our trucks need to have a scanner with a Library containing both the Ford Proprietary AND the Diesel Specific codes in it. Add to that, our trucks are Not, specifically, OBD-II so the Generic scanners the Auto Parts Stores have are of little use to us. But today there are some very good App based tools, that are close to what the pro tools do, for fraction of the cost.
Once properly equipped, you can check vital engine sensors and compare their values between when it will & will Not start. For the $30, it's a smart investment