Tach accuracy issue after mods

[Dominus]

Hi there!
Currently the stock tach on my 94' EJ1 has turn very inaccurate.
Stock ECU was replaced.
The car is equipped with a AEM EMS stand alone and when tach is at 5.5K rpm, the engine is really spinning at 7.2K rpm.
Also I have a shift light wired to the ignitor and a VTEC light connected from the VTEC solenoid signal.
This issue didn't exist before a complete engine disassemble, all motor rebuild and Alpha -N mode tune with ITB's and all the facts stated above.
-Bad/poor grounding on the tach?
-Rotor screw, bad rotor, connections, etc?
-Ignitor going bad?

Thanks a lot in advance!