I have had cases where a bump causes stalling and have found the culprit to be the CPS. Even a small bump like when you leave the garage floor can cause it to kill the engine. In this case it would restart and act normal until next bump. Inside the CPS there is a Hall sensor which have sensitive components that could fail after years of use. As stated above, this problem could be caused by various of different things, but I will mention the CPS due to my earlier findings.
Helge

lol, you are right. I missed that one. My bad indeed. I reckon he allready have sold the truck by now.