Transmission does not shift properly into sixth gear?

Yep, this happens when the clutch actuators go out. You can drive it in 5th gear but the engine will have a higher RPMs so it will wear the engine out faster and give you poor gas mileage. We should run the codes to confirm the issue, this guide will help:

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Here is how to swap the actuators out in case a code comes up for it. Replacing them
both should fix the problem. Check out the images (below). Please let us know what you find.