2000 blazer 2wd shifting problem

i'm having some trouble diagnosing a problem with my blazer. when i'm driving around the neighborhood the truck seems to shift at a higher rpm that it usually does. when it does shift it will wind up a little farther than it usually does and then shift hard. there is no noise to speak of and everything works but i was wondering if my tranny might be going out or what. just change the fluid or tranny filter? any help appreciated. oh truck has 103,000 miles

First, check your fluid, also is the check engine light on?