In your experience is changing Transmission and diff oil needed??????????
My apologies. I got the wrong end of the stick there. The next step for me will be replacing the gearbox oil, but not at Hyundai inflated prices of £48.00 per litre. I've gone for Red Line MT-LV oil, they list it as a direct replacement to the OE. A helpful member who resides in the USA uses it in his veloster N and says it improves the gear change immensely when cold and gets rid of any baulking.
I got it from Opie Oils.