For about a week now I have noticed my battery light going on and off. As of yesterday, my RPM's are now dropping for no reason. I'm staying at the same speed, and my rpm's drop down to 2....when they should be at 3. I'm not hitting the brake, or taking my foot off of the gas pedal. I had both battery and alternator tested, and they are fine. Has anyone had this problem, or have any idea what could be wrong?

Thank you!