renualt mascott cuts out at 300rpm?

it a 57 plate mascott with the 3.0 nissan engine had troudle starting it for a few days in the morning but once started it would restart fine, then
started cutting out completly under load at 3000rpm but will restart again straight away took it to a renault dealer who have replaced the leakoff pipes, the 4 injectors ,high pressure pump sensor, fuel filter, and the common rail but still havent fixed the fault and are know surggesting i scrap the truck??? HELP PLEASE