The problem you have is not a mechanical issue mostly, the "DCU" aka diesel engine control unit - more called ECU needs to be interrogated and recorded for feedback to what its doing with the engine.
The injectors on this engine have build codes on them which need to be written to the ECU to compensate for flow rate - its not an ustaad shaagird scrap/kabli parts job. The fuel pressure in the fuel rail is maintained by a dump valve and is sensed by a pressure sensor too - both of those parts have been updated by Toyota worldwide (scrap and surplus parts wont be updated)
Best go to toyota and talk to their service advisors first and let them know that you want the fuelling checked - please be wary that they MAY completely refuse this service as this truck was not imported by Indus Motors Co. Pakistan.
Independant shops may do this job for you but make sure they have the correct scan/write tools for this job.