Are you having acelleration problems? Problems hifting into gear?????
Clunking is not nesicarly tranny....Could be axles going bad, control arm going bad or the tie rods going bad....id save tranny as a last resort before going that far.
Its best to use a proper process of elimination starting with the easiest to diagnose (what i mentioned above) and then working your way up....
Jack up the car, look at the tie rods and see if there lose, see if the Control arm busing is torn, and check the CV boot on the axles to see if there torn.
Start there then report back.
Lupe