Chevrolet Silverado

1996 Chevrolet Silverado C2500 w/6.5 liter Turbo Diesel, 4 speed Auto, with 226,000 miles.
At random intervals the engine cuts out while driving - although this occurs most often at around a half a tank of fuel. I have replaced fuel filter, in-line fuel pump and fuel cap. Often right before the engine cuts out, the " Service Engine" light comes on, but there are no error code (I have had this checked multiple times) or error code history in the on-board computer. Additionally, there have been a number of occasions when the engine hesitates once or twice about a mile before it cuts out. I have taken the truck to the Chevy dealer and they have no idea what the problem is - can you make some suggestions as to what to try next.
September 17, 2007.

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