Improve reading speed at advanced level
Hacking Chinese (by Olle Linge) mentions that the way to reading faster is to simply read more. Presumably extensive reading as opposed to intensive reading. That is, read many different texts that are well within your ability to read, as opposed to a few texts that are closer to the edge of your ability to read. By well within your ability to read, I mean that you know 98% of the words (not simply 98% of the characters). By reading extensively, you will be practising reading texts as opposed to practising studying them (i.e. looking up a lot of words or grammar, or frequently stopping and thinking in order to understand the text).
You could find easy texts (such as graded readers) and read (and re-read) those until you can read them at the speed you would like. Then, you could slowly increase the difficulty of the texts to improve your reading speed on more difficult texts as well.
Hacking Chinese goes into more nuances and has more advice in their articles, but I understand extensive reading to be the main thrust of the approach to improve reading speed.