Does not shift into Drive when cold, shifts very hard between 2nd and 3rd gear.

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Hi there. I'm from South Africa. My Tucson will not shift into "Drive" when the car is cold, only after it is warmed up. Then during the first couple of kilometers it shifts hard from second to third gear. This only happens between 2nd and 3rd gear. After a few kilometers it is fine for the rest of the day. Engine check light also comes on regularly. I've taken it to the dealer on 3 occasions already but still no answers. Transmission fluid and filters are checked. Now they want me to replace the whole gearbox. If heard about a problem with the computer software. Could this be?