All the mountain ranges you listed—the Sierra Nevada, Appalachian, Cascade, and Rocky Mountains—are generally associated with highlands climate regions due to their elevation and the climatic changes that occur over short distances. Therefore, none of these mountain ranges can be definitively classified as "not in the highlands climate region."
However, if you are looking for a mountain range that might have milder or less pronounced highland climatic conditions compared to the others, the Appalachian Mountains tend to have a more tempered climate, especially in comparison to the much higher Sierra Nevada, Cascade, and Rocky Mountains. That being said, all of these ranges do exhibit highland characteristics to some extent.
If you're looking for a clear answer regarding which is least representative of highlands climate, it would likely be the Appalachian Mountains.