What could be wrong with it?

I've got a 93 chevy c1500. One day, it wouldn't start. Just clicked as I turned the ignition. He seemed confident it was the starter. So we had it tested, it failed, bought a new one, the car ran for the rest of the day. Then this morning it was back to clicking. The starter couldn't have gone bad again already, right? Not after just one day. Any ideas what else it might be? It's not just battery. Everything is lighting and sounding off just fine. Even got a new battery just in case.