Problem: The car will not stay in 5th gear with the torque converter locked up when encountering the slightest incline while the cruise control is activated. Instead, the car will 5-4 shift, unlock the converter, go awhile, do a 4-5 shift, then do a 5-4 shift, so on and so forth. This is an undesired operation of the engine/transmission ONLY while the cruise control is activated. This has happen on eight of the 2009 Sonata's I have experimented with.
If the cruise control is OFF and you are just using the gas pedal, the trans will stay in 5th gear, and the torque converter will stay locked, on even bigger hills, and you can even accellerate gently without the transmission doing a downshift. This is the desired operation of the engine/trans that should also happen when the cruise control is enabled.
I have asked the dealer to fix this problem so the the cruise control operation of the transmission/engine will more closely pattern itself to non-cruise control operation. They say that they cannot because Hyundai USA has not released a software upgrade to fix the problem even though the vehicle is a one model year old and the 2010's are programed the same.
If this is happening to you, find it irritating and fuel inefficient, and you would like it fixed, I encourage you to inform your dealer and to call Hyundai USA customer service at 800-633-5151 and make your wishes known. (Their phone number & address are at