2006 Kia Sorento Electrical

Hello, sometimes, not all of the time I turn the key to start and the starter doesn't "turn" the car over.I just get all of the dash lights, if I keep turning the key to start it sometimes it will turn the engine over fast sometimes fast, sometimes slow! I had the battery, and the alternator tested, both are good.I looked at the terminals, and the starter for corrosion, none there.I at first thought I was the battery so I ran a 6amp charge on it showed full charge(engine running) but everytime the voltage regulator would "kick in" to charge the needle on the charger would "flip" to the no charge side until the regular released its charging state of contact. Is that normal, any idea's for me, and thank you! Glenn