I suspect the "new" injectors you got are faulty. You said that the engine ran worse with the "new" injector than with the injectors that are very old, and that doesn't make much sense unless there is something wrong with the new ones.

I would bring the old ones to a shop and have them tested, and then probably rebuilt. I would not do the IP test at this point. First, it's a bunch of fun to remove and reinstall. Second, it's going to cost more to test the IP than the injectors, I would guess.

Conclusion. Test the injectors and don't take anyone's word for their condition other than a reputable diesel injection shop (or buy rebuild ones from fastlane)

240Joe