2000 NPR keeps dying
 

My 2000 NPR diesel had been on a tow truck 6 times for the same issue. It started when I got a plastic bag in my fuel tank (lost cap) and even after removing it I continue to have the same problem. Truck runs great, then will Lise power and die. I had the lines Ed and it ran fine for a week or so and then died. Towed back to a different mechanic who cleaned the tank of a little debris, changed the fuel filter then cleaned the tank vent. It ran great for a week and a half and it died again today.
Any ideas?!
thank you!