I don't know about Mitsis, but from the Landcruiser forums when people completely block off the EGR valve it does throw issues and is inclined to put the EML on, the answer appears to be drilling a certain sized hole in the blanking plate allowing enough by pass to keep the system happy.

Obviously this is nothing to do with Mitsi, but i suggest the answer to this is more likely to be found on one of the Mitsi 4x4 forums.

If funds are tight, i'd first suggest removing the blanking plate and let the EGR do its job again and see if it make any difference.

Good suggestion re a Diesel specialist, again the forums should be good for this or ask around taxi drivers and the like where you live, if it does prove to be the pump then catching this soon before total failure is more likely to mean the pump can be rebuilt.