Inconsistent engine failure

At the shop I work at we have a '97 model. I haven't been working there long, but the two other guys have been working on diesel engines for over twenty years, and this is still making them want to pull their hair out (what they haven't lost already).
Sometimes it will start and run just fine. We've had it running idle for an hour and a half, drove it for about thirty minutes, then shut it off and let it sit for an hour or two and it wouldn't start back up. A few times it would die while it was running and wouldn't start back up. Sometimes it will start, but sometimes it won't. Very confusing.
No codes show up on the scanner. It still has power to the shutdown solenoid. It has a new lift pump and fuel filter. It almost acts like it's not getting any fuel, but we took the fuel return line loose (it was it one of it's "running" moods... took it loose, started it, shut it off, then reconnected it) today and it didn't affect it.
If anyone has any suggestions... please help out. Sometimes I feel helpless not knowing what to do, but I know that two well experienced mechanics are getting flustered not being able to figure this out.

~damiEn~

Intermittently on my 96 Express the lights would dim all of a sudden, and the van would just die. Some times it would start right up, sometimes not. It worsened to the point where intermittently it would not start. The battery always tested fine. And it seemed like a poor ground. The cables all looked perfect and the van was exceptionally clean.

It turned out that my battery connections were bad in spite of the fact that they were free of corrosion and tightly secured. The negative terminal has 2 wires connected to it and there was a lot of rubber/plastic material in between them that was acting as an insulator. After I cracked them apart and scraped them, all was just fine. Hope this helps. Any info on my post would be appreciated.

Rob

I assume your working with a 97 van with a 6.5 diesel (turbo?) with the
computor controlled injection pump and the electronic fuel (gas) pedal.
The usual cause (in my expieriance) is a bad driver module-the black box mounted on the side of the injection pump. Don't know where your at,but you may want to contact your local GM dealer.They won't admit to a problem, but many vehicles have been repaired under a extended warrenty that the average consumer does not know about.
Hope this helps.

I had the same problem with my 97 van with the 5.7L. Drove me nuts and any mechanics I took it to. As someone already stated, check your positive battery connection under the red boot. Both paddles are joined there and between the paddles is where your going to find corrosion. I have to clean this about twice a year. Mine finally got so bad that it blew loudly and wouldn't restart at all........while driving out of Yellowstone Park in Wyoming with a herd of buffalo crossing the road.