Transmission Question
 

I have a Jeep Cherokee Trailhawk 2.4L and the thing I have notices is with city driving all is good but as soon as you go on the highway for about 1 hour the odd time the rpms go high then the Service transmission light will come on and seems to loose power. Any ideas why this would just happen on the highway and since Jeep says that you dont have to change the lifetime transmission fluid would that mean the the transmission is warranty for life... Thanks