I didn't read that you pop-tested the injectors. The main thing that would cause unburnt fuel is a bad spray pattern like a streamer or a leak when closed. I doubt that mis-matched pop pressures would explain your symptoms since I recently found 3 of 5 injectors in my 1984 were non-turbo (1600 psig), but the engine had run fine like that for years.

If the injectors spray OK, my next suspicion would be the IP. Perhaps someone put the delivery valve parts in #1 back wrong after a "start of delivery" check. With the engine idling, loosen the tube nut and each injector and see if each cylinder contributes the same. It should idle pretty rough with each cylinder disabled.

Finally, while the injectors are out, inspect each pre-chamber with a video camera. I have a small USB "endoscope" one I got for $18 on ebay. It has an integral LED light. I haven't tried it on pre-chambers yet, but it shows my tonsils well. Should also work to search for hemorroids (yuck).