Had a Performance distributor coil start to go bad on me a couple of years ago. The tach display would jump all over and it ran poorly. Put a new coil on it and it ran normally. If the tach signal is jumping around make sure your connection is good, but you might also test your coil, they do go...
When the ECM controls the distributor it advances or retards the spark as needed based on driving conditions and feedback from the sensors (O2, MAP, etc.) so it 'should' provide better drive-ability, fuel burn and reduced emissions.
I pieced my system together using a Howell computer I found...