engine sounds like its running way too hard when driving forty mph

When driving forty mph and up the engine sounds like its running way too hard. No check engine or any other lights. When driving up a hill at the above referenced mph there is significant power loss. I can be going sixty mph and up a hill speed will drop to forty mph.

Regular oil changes, all fluids are fine. I love no idea when a tuneup was last done.

Otherwise I have owned the vehicle for six years with zero repairs or issues.