2000 Buick Century car jumping between gears after driving

I have a Buick Century 2000 Limited and for some reason after driving around town for awhile my car will start jumping when going from 1st to second and sometimes from 2nd to 3rd gear (It is an automatic) it also will make a different sound in the engine (not too out of the norm but, just different). It has done this now for over a year.......I know I know.......but, since I do most of driving on the interstate I have rarely noticed it. Now it seems it is doing it in higher gears and not just during city driving.

My engine doesn't appear to be getting hotter but, I do smell something that appears to be rubber like.

Any ideas?