Here, it may be because of the tumbling media. If you have been using the same tumbling media for many years, you will be using beyond its life. So, it is time to replace the media. If the abrasive properties of the media are lost, it will take a long time to finish the parts. The other problem can be the media to part ratio. If you are using fewer media in the bowl, then it will take a longer time to process. So, it can be either of these problems, which you need to figure out.