99 Navigator Slow Cranking up

Ok, I have a 99 Navigator. For several months now it has taken several seconds for it to crank up, when it used to just start right up. When it is warm, sometimes it will still crank right up. I've had the alternator and battery tested and they are just fine. Does anybody know what it could be? thanks

Did you have the battery load tested? Are both ends of the battery cables clean and secure? When was your last tune-up?