i have a 95 mustang V6 auto. it has 132,000 miles and the trans mission was slipping a lot around 30mph and 45mph, for example i would be driving at 50mph and the rpms would go up to 4000rpm, and also when i was braking i could feel a little clunk in at 35mph, but it only did this a couple times a week. So i got a used trans with 62,000 miles (with torque converter) that had no problems etc. etc. and now it still slipped but not much, just a little bit every once and awhile, it doesnt clunk in when i slow down either. Any ideas what this could be?

thanks,
steve