Need to know more about Torque converter.?

We have a 1998 Plymouth Grand Voyager thats service light has been on for a little while ocasionally the car will stumble when shifting gears this is not a constant thing though and we have no stalling problems. We were told it needed a new torque converter but from reading other things on torque converters it sounds a little different than those testimonials. Anyway is there any chance it could be something else( we have changed the transmission fluid it stops stumbling for a little but then comes back) and about how much will it cost?