Kia Troubleshooting Questions? Ask a Mechanic
It sounds to me like the transmission is just starting to show signs of normal wear. How many miles do you have on the vehicle?
How long has it been since the last time the transmission fluid was replaced?
Does it seem to slip when shifting between gears or at high RPM?
If it only slips slightly and when going from park to drive or reverse then I would say it's either normal wear or a slight fluid restriction.
You could have the valve body disassembled and check for sticking solenoids or valves, or you could have the transmission pan dropped to make sure the filter isn't cracked or poorly seated in the valve body.