I have seen some strange activity on very large text files. It has to rewrite the entire thing and may take a while.
Otherwise, the down arrow, if you are referring to a scroll bar, does only one line at a time. But if it hesitates after you click the space or do a page down, it is not refreshing quickly.
Do these text files have any type of links in them or something that has to be gotten from online? I suppose there are no graphics since you say text file.
What utility are you using to view them? Could it be having a problem with the font or format?
Where did the text files come from? If you downloaded them, you might check the properties and see if they are still blocked.