Are you sure the injectors and rails are clean? Not to mention the lines to them? This could simply be a supply issue, but usually you see that with rpms on top of off idle. You could even have rusted up intake valves not seating. That's the whole reason I mentioned mechanical issues to begin with because what you're experiencing is often enough associated with compression, valve seal and general base fueling issues. Especially if it had that kind of damage in the fuel system already. Injectors can look clean but still not flow correctly. They could even be sticking a little.