1995 Chevy Truck COMPLAINT OF SHUTTING OFF THEN STARTING BA

VIN #1GBJC34FXSE192064 / 6.5L TURBO DIESEL
Truck is an unfinished chassis with a food delivery box mounted on it, the type with the gull wing doors. Truck was towed in today and I talked with the driver; he said he was on the route about 5 hours when all of a sudden the engine shut off. He waited a minute and then restarted the engine. It then ran a few minutes then shut off again; he repeated the same procedure and it started. It did it twice more but would only run a few seconds before it shut off. I got to the truck and it started immediately; I checked all the fluid levels, there were no dash lights or DTC's showing. I checked the engine performance repair history; the oil pressure sensor that feeds power to the fuel pump was changed 04/29/08 @ 351,045 mi & the fuel pump was replaced on 07/07/08 @ 352,955 miles. Both batteries have been changed in the past 16 months; I load tested each battery as well as the start/charge systems and everything passed. I hooked a pressure gauge to the fuel bleeder port that is mounted on the front of the engine on top of the thermostat housing & checked pressures;
1. At warm idle; 5" vacuum @ 800 rpm
2. At cruise (45 mph/1700 rpm) - 2 psi pressure tops.
3. Sitting in park; 1.5 psi @ 1700 rpm idle, goes right back
to 5" vacuum when off throttle (idle, 800 rpm)
These figures really sound off the wall; not sure I understand how it can run so good with figures like them.
I ran the engine for approx. 30-45 minutes then drove it for approximately 30 minutes and it never once acted up or gave any indication of shutdown. I trust the driver and know he wouldn't make up a story like this so there has to be some problem somewhere, I'm just not sure where to go next because I don't have intimate knowledge or experience with the electronics on this diesel engine. I couldn't read the codes because my reader only works on 1995 up and has the wrong harness plug; could you give me the procedure for paper-clipping the codes? Also any other suggestions; have to go back to the truck tomorrow and need to get it fixed.