Sept. 2010 is a 2011 model. Whatever, what engine do you have? Does your trans have 'Sport Shift' or whatever they call it where you flip the shifter to the left and you can manually shift the trans? Do you have a transmission dip stick for checking the trans oil? Our versions do not - there is no trans fluid checking without getting under the car and unscrewing the fill plug. Its filled with special fluid and normally would not be checked before 100,000 miles. If yours can be checked, find out how to (engine off or running) and see that the level is correct and the fluid is not discolored or burnt-smelling.
Was the battery disconnected or replaced at any time since you've had the car? Try driving it harder for a few days - give it more throttle when moving off and hold the pedal in the same position to the extent you can while driving safely and legally.
I doubt if there is anything mechanically wrong with it, but it could need re-flashing (reprogrammed). Here's another thing I might do - disconnect the battery for a few minutes and reconnect it. The car will drive a little differently until it learns how you drive. Drive it hard during that period and see if the trans does anything funny.
Many computer-controlled tranmissions today will sometimes get a little 'confused' during light-throttle driving and you may get unexpected 'flares' between gears and a harder engagement. These things are normal if they only happen every so often. That's why I suggested driving harder to see what happens, to prove that the trans is mechanically sound.
2011 Sportage EX
FWD Auto Silver/Black