Unhappy about repairs on my NP300

Hi I ve send my bakkie in for repairs at the dealership knowing that they are the expert in this field. First I was told that the problem was an faulty diesel pump on the bakkie. Luckily there was an extended warrenty to cover this.(I had to pay for the filters) Got it back and after a week or so the same problem. It keeps on stalling after driven a couple of km. Then it was the fuel line witch was cleaned but still the same. Took it back and then the new manager told me that this is an old issue with the NP300 and that he says that its the LIFTER PUMP,(witch I had to pay on suspicion of the manager. I paid only half price thanks to Nissan SA) so it was changed. Again after a week or so the same problem. I was told that specialists will be coming out to inspect and fix the issue but as we speak now the NP300 is yet back at Nissan due to the same issue. Now is this about a guessing game on what the real problem is or is there anyone that can fix my NP300. The PROBLEM is my wife drives this vehicle and WHAT IF she gets stuck next to the road??? I sit on this end paying for all with suggestions for the problem. Is this incompetence on problem solving or what? Please help with this?