When I roll up the windows, or rev the engine, all the interior lights dim, headlights dim, and the voltage indicator on the dash drops below the 12volt mark. As part of the troubleshooting I removed the alternator and had it tested. It came up mostly dead, so I replaced it, but the dimming thing and dropping voltage hasn't stopped. The truck starts right up, and has never died on me so I don't THINK it's the battery. I'm concerned that I'm seeing the tip of the iceberg, but not sure where to go next. Ideas on what I should check, or if I'm just being paranoid?