The injector tubes, or as Cummins calls them, the connector tubes are pretty strong. The biggest problem I've seen, from experience, is the fuel lines. Once they are bent back slightly from their seated position, in order to partially slide out the tubes and so remove the injectors, it can be hard to get the ends of the fuel lines re-aligned and seated correctly in the bevelled end of the tube. To prevent bending the fuel lines as much as possible, almost all of the brackets holding them have to be unbolted. Then, when re-installing, the line has to be held in against the tube, while you snug the fitting nut tight. Proper torque is a must, over-torqueing can deform the end of the fuel line, maybe even block it partially. The #4 line has given me the most trouble.
Other than the fuel lines, I'd have to say one of the injectors either has some dirt in it, or is defective... it's not hard to contaminate the injectors, I've been told by quite a few diesel mechanics. Steve, maybe a trip to Dave's Diesel in Muncie would be a good idea? They can check pressures for you, or even check the injectors individually. (you might have to remove them to have them "benched")
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