That was a good hint A & C and the likely cause. We took the injector lines off, had small glasses and ran the boost pump, comparing the amount of fuel in each glass to find the same fault.
One that really drove people crazy, was a broken inner exhaust valve spring. Fine at idle, then a growing vibration to a real shudder, dropping away and then coming back in a pattern. If your vibration or "rough" running has this sort of pattern, and the injectors check out, you could check this as well.
Good luck