In looking at video tutorials on the use of this tool, I noticed that the presenter had a quick response when using the smudge tool to stretch out parts of an image.
When I use it, it takes quite a few seconds to do the same stretching. Have I made a mistake in the use of the tool? Could it be caused by the speed of my computer's processor?
It could be your processor / GPU speed but it could also be as simple as the pixel size of the image and the size (in pixels of the brush).
Highly likely your computing power / size of file. How much RAM do you have ( should have a min. of 8GB ).