By engine sensors, does this include all of the IP sensors? I would use a DMM and the factory manual to check the IP sensors. I know they're either 5 or 6 sensors on the IP.
For what its worth, there is a company here in Southern California, Becs Pacific Diesel. This is the route I went when I was having problems, I had them rebuild the IP. Included new sensors and dialed in on their bench tester with a new spill valve and fuel screw adjustment. Also make sure the connectors going to all the plugs are on snug, another thing to check are all of the pins in the connectors to make sure they are making complete contact. I had a couple pins that were opened up too much, not making complete contact and caused random problems.
Hope this is a start, Let me know if you need the manual for the 1kzt-e I have it saved on the computer here.