I'd say your tranny is about to shit the bed. I wouldn't do a drain-and-fill to your tranny now, all I would do at this point is check the level when it's hot and add if you need to. At this point your fluid is probebly close to black in color and if you do drain the case then you'll also drain out the friction material that is in the fluid from the clutches inside. Now when you fill it back up with clean fluid you might not get the fluid and clutches to mesh right and the car possibly won't move.