Diesel truck dies, chevy, not mine
We have a small fleet of service cube vans at work most are gm 6.5 diesels, a few of them had been doing the same thing with no codes when checked, I think some of them were traced back to the computer being faulty. Same thing happening the engine would just shut off and restart with no problem. Its a tough thing to figure out as usually if you starve from lack of fuel the engine will require some cranking to get going again, restarting right away without hesitation usually leeds back to something electrical which is like a needle in a hay stack. Tell your bud good luck, these gm diesels are junk compared to the Cummins or the Mercedes in the Sprinter vans. Check on the web I'm sure there's a forum somewhere with the real experts.