truck dies on highway: help!!

[thaddad]

4 times in the last year my truck has died. It is a 93 Dodge W-350 with Cummins Diesel. The first time it happened I checked the filter and it was full of fuel. After towing it back to my shop I cracked all the injector lines and it had fuel spraying as far as the bottom of the hood. After much head scratching I went home for the night and didn't sleep well thinking about it. The next morning I checked the shutoff solenoid it clicked and had power. I cracked one injector line and turned the key and the truck started. I drove the truck with the same half tank off fuel and could not get it to die again. I changed the lift pump and the filter as routine maintenance. (The pump was weeping oil). The truck ran fine for 10 months. One month ago it died again while pulling a hill in 4th gear. It acts as though it runs out of fuel. The filter is full when this happens and the hand pump has no affect as the system is pumped up to pressure already. I cracked 4 lines and cranked until all the air and froth was gone. Tighten the lines and the truck starts. It clears up after 30 seconds or a minute just like when you change a filter and have to work out the air. This also happened twice 2 days ago and bleeding makes it start. I have also pulled the lines 3 times and cranked it to see if any injectors blow bubbles. All have been fine everytime. My theory is that a nozzle hangs open and the cylinder pumps air back to the injector pump killing the engine. Has anyone seen an injector do this??? How do I isolate the bad one or do I change all of them? Any help would be appreciated as this is my tow truck for my business. Thank you Tim