I have a 2008 Nissan Alitma with about 133,000 miles now. Over the last 4 years over long distances, I have been driving only on the highway and I have it in the manual setting and I notice when I go to down shift, it will not downshift and then I try to accelerate and I have to push the peddle to the floor for it to 30 seconds later start picking up speed slowly but my RPMs are very very high and I am not even picking up enough speed. It only does this on long distances. I stay local I am find but longer than 30 minutes it will always do this. I have tried driving the car in the automatic setting and it does not matter it will happen. The only way I can basically reset it for lack of a better word, is leaving my car off for a extended period of time. I have brought it to mechanics and basically they say there is nothing wrong with it. I also hear a loud for lack of better word high pitch whining noise when it does it. Any help with this issue would be greatly appreciated.

I'm going to move this to the Altima forum instead of the Z forum.
The altima has a CVT, so the high RPM thing under heavy throttle is normal. Do you have the 4 cylinder or 6 cylinder engine? Do you happen to have a video of the speedometer and tach when you go full throttle (when the problem exists)?