99 trans doesn't know what gear to be in

I have a 99 6 cyl auto. The transmission doesn't seem to know what gear it wants to be in. I have searched for a tranmission control module but haven't had any luck. Is there such a thing on the cougar or does it work off solenoids or what. Does the ECM control any of the shifting? Is there a way to check the codes and see if it shows anything or not? I am not sure how long it has been since the trans fluild was changed. Thanks for any/all info and suggestions.