Diesel truck dies, chevy, not mine

A friend at work has a 94 6.5 turbo diesel truck. Says it will just die as he is driving down the road. He will pull over and it starts right back up and runs like nothing happened. But it keeps on doing it... He did take it to a shop and they said they couldn't find any codes coming. Any ideas or is there a good site to go to to ask about this problem