Taking notes allows you to reshape the content of each topic you study from the textbook in your own personal way. And so taking notes is absolutely vital to good studying.
A better approach is to read a paragraph, close the textbook, and rewrite the essence of the paragraph in your own words, or better still using a mixture of pictorial symbols and verbal words. That way, you might retain the information for a longer period of time.
Also, it's a good idea to skim read an entire chunk of text that you feel encapsulates a single major concept of the topic you're studying, and then to read it again until you get the gist of it. Then you might want to read it carefully. Afterwards, you might wish to see if you could present the same thing in a way that seems more logical and natural to you, i.e. reshuffle the various chunks of text in such a way as to make you feel that the argument flows naturally. You know you've understood the concept when you find that if you're given the first and last sentence of your notes, you can reproduce all the intermediate sentences because your presentation of the same argument happens to flow just naturally and logically.
If you're in a hurry to finish a textbook, you might just wish to time yourself per page, say, 30 minutes per page. That way, when your 30 minutes are up, you're forced to move to the next page regardless of whether you understand all of that page or not. Usually, for me, I understand 80% of the page and I highlight (whatever of the page I don't understand) in the notes with a pencil. Once I revise my notes and its highlighted parts a week later, everything happens to fall in place (eventually). Deep understanding takes time, so no matter how much time you spend on a single page, you won't get better understanding in the short-term. So, speed reading is probably the best strategy because you know that when you come back to revise your notes, what you did not understand the first time will gradually begin to make sense. And anyway, it is not possible to understand/impractical to want to understand 100% of a textbook. Achieving a 90% understanding is sufficient and you can move on to the next textbook.