F250 Stalls for no apparent reason

I have a friend who owns a 2000 F250 Heavy Duty diesel pickup. Very recently he has been having problems with the engine dying for no reason whatsoever. He can go days without it dying, and then at the most inopportune moments, it's dead. He replaced the fuel filter a year ago, so doesn't think that's the problem. He still has battery power, lights, etc...but no engine. I told him I thought it was sucking air in the fuel line and confirmed this with my father who teaches Diesel mechanics at Chatahoochee tech. However, dad is 2500 miles away and can't help. Can anyone tell me if they have had this problem, and where we can find some diagrams of the engine...he is a single dad of 4 and recently unemployed so a "REAL" mechanic is out of the question. Thanks!