I have been having a problem with a 2008 5 speed auto doing the same thing. I have been to the dealer 5 times. 4 out of the 5 times the car ran fine when got there, no codes. Yesterday I drove 45 miles stuck in 3rd gear, this time they drove it and stated it was stuck in 3rd gear and there were no codes.
By the way on my 4th time into the shop I had the transmission flushed and new fluid to the tune of $200.00 it was of no help as you can see.
Their fix is to unplug the transmission and to plug it back in... This is getting me very upset... In 400 miles Im out of warranty because I bought the truck used... It will hit 60,000... Im not a happy camper, If this does not fix the problem Im going to trade this in and let some other poor slob fix it. I Love the way it runs and drives but with only one vehicle I need a vehicle I can count on, I will walk away from KIA for good! This is my second Sorento The first was great.
By the way this has been going on for a year now.