2004 Chevy Cavalier Ignition Coil

Have already put in a new starter, starter cylinoid, battery, and had alternater test which shows now problems. Still have problem where sometimes the car starts and sometimes it doesn not. Sounds like a VERY low battery, but battery is fine, and still charged. When you jump the car across the post on the starter, it starts just fine. I'm hearing it could be the "ignition module". Where is this, and how do I test this?