i have no experience with the car you are using, but since the problem starts when you drive it at high speeds. i think having your clutch, presure plates checked would be good idea, since the sounds when you release the cluch. if you are going for gear box repair, first check in the market if the parts are available in market because there are going to be some things that will have to be changed for certain if the box is opened. you can mongomery road for parts i know there are some shops dealing kia.