2007 Ford Freestyle Odd CVT operation

I have a 2007 Ford Freestyle 3.0L V6 FWD with the CVT. Just recently, I noticed the RPM will be about 500-1000 above where they should be while driving on the highway. City driving seems to be ok. If I'm driving 60MPH instead of cruising at 1900 RPM, it will be at 2500-2800 RPM. If I go up to 70 MPH, then RPM is around 3000. There are no warning lights, no wrench light, no error messages. I have had no surging or lunging at all. Reverse gear works well. I have normal acceleration from a stop or passing and no notable loss of power. However, when on the highway, if I do pass when the issue is occurring, the RPM will go up to say 4500 or more according to my throttle use, but will take a long time to return to even 3000 RPM. Gas mileage seems about normal. I noticed that the issue tends to happen when the vehicle is at operating temperatures and "shifts" fine just after starting or seems to return to normal if I've been driving the highway for a couple hours or a come to a stop then continue. I've heard anything from bad transmission to dirty throttle body. Any possible ideas and advice would be of great help.