Well, you could try swapping the #3 injector to a different cyl and see if it follows the injector. I assume the injector seals were replaced, but you could carefully spray some carb clean at the injector seal area to try to find a vacuum leak there. As far as a secondary ignition problem, ideally you should get it in a failed state while on a ignition scope. Did you use good quality cap and rotor?
The fuel injection cleaner is called Techron, made by Chevron, and yes it's pretty good stuff.