automatic gearbox problem on TD5

Hi-new to this forum and trying to find my way around the site-have run a TD5 ES Premium for the past 170000 miles-it developed a clunky box at low speeds many miles ago but the problem didn't seem to worsen so I ignored it-have recenly replaced it with a "new"one-only done 62000 miles but seems to be developing a similar problem-jerky changes at low speeds in traffic-is this a feature of the TD5 and can it be remedied inexpensivly?