engine surge

Let me preface this post by saying I have done a lot of research and have not found any help on my situation. I'll continually search for an answer even beyond what advice you people may have if I can not find a way to solve it. If I do manage to solve it, I will put a post explaining how and...

I have an 07 rendezvous. The rpm's will jump around 500 while driving normally causing the car to jerk. If you push the gas further it will downshift and speed up, but once you go back to cruising speed it will jerk. The problem used to only be at higher speeds around 70, but now it does it even...