Kia Optima Gearbox & Transmission Problems
Kia Optima transmission oil
Changing the transmission oil regularly is a good thing to do, it will keep the transmission alive and well for many thousands of kilometres to come.
Transmission flaring in Kia Optima
The transmission is designed to adapt its shifting pattern to your driving style, which I assume is slow and steady given that you have only done 34,000 km in six years of owning the car, and that's probably what you're feeling, as Kia has suggested. Having the gearbox serviced and the fluid changed would be a good idea, but I suspect it wouldn't fix your problem.