1995 Chevy Corsica charging problems

Recently I was driving on the highway driving back home, and the battery light came on as I was driving, which I knew meant the car wasn't charging anymore. I was only about 5 miles from home so I decided to just push on home instead of stopping on the side of the highway. Needless to say by the time I made it to town there was barely any power left in the battery to keep the car running. So the next day I changed the battery and the alternator, but it is still having charging issues. I had them both tested, and they passed. So i'm wondering what else it could be. Any idea's?