Great question. There is one thing that might be an easier fix—though whether it will work for you depends on why you're finding that your reading speed is slower than you'd like. Otherwise, there is a way to improve, but it's likely going to take a couple of months.
A lot of people try to read/understand every single detail very carefully when reading on the GMAT—which you don't have time to do on the RC or MSR portions of the test. If you're trying to do this, then the task is to learn how to distinguish between what you do need to pay closer attention to and what you can mostly ignore (or just understand at a high level) on your first read-through. If you have our All the Verbal book, we talk about this in the RC unit of the book—that you're reading initially for the main story, but you're mostly skimming the details. And you only come back to those details if/when you get a question about them.
Because you said that you're also having these issues on CR, though, I'm going to guess that you're more likely to fall into the second category—that you really do need to improve your reading speed on everything. In this case, the best approach involves improving your reading speed overall / on anything, not just for the GMAT. This does take some time to develop, but the skills will help you in grad school itself and in your personal and professional lives in general.

The goal is to read university-level source material for at least half an hour every day. I'll give you some good sources below, but I'm first going to talk about what to do.
Read something for a few minutes, jotting down *very* light notes as you go, then pause and summarize *out loud* what you just read. Pretend you're talking to a friend and you want to give them the main ideas of whatever you just read. (Or talk to your cat or dog or whoever.

) Then read some more and do the same—but this time, both summarize the new information you read and, when appropriate, add in any connections to the earlier portions of what you read. That might be something like:
1st read: The article is talking about a problem with bees. Bee colonies are dying off at a faster rate than normal and there are two main hypotheses about why this is happening: (1) pesticides and (2) viral infection.
2nd read: The author presents the case for the first hypothesis, pesticices. There is at least one good reason to think that this could be the cause, but there are some other reasons to think it's not necessarily pesticides. The author doesn't actually say that pesticides aren't the cause, but they seem to be doubting this hypothesis a bit.
3rd read: The author presents the case for viral infection. Again, there are supporting factors but also some things that make it seem like it might not be viral infection, either. Hmm, let me check the beginning again...the author only mentions these two as the main hypotheses, so that seems a little weird. Maybe the author is just going to say that we don't have enough evidence yet to tell which hypothesis is the right one?
4th read: Ohhh, I see. The author is now presenting an entirely new third hypothesis: noise pollution. Basically, the "industrial hum" of humans is somehow harming the bees' ability to navigate. Ok, so the overall message here is that there are two main hypotheses that most people talk about, but this author is advocating to consider this third hypothesis as well.
Keep doing that until you've either read the entire article or until you've read about 4-8 cycles / until you feel like you've gotten to a point where you've got a good handle on the overall "story." Then pause and look back over everything. What's the 1-2 sentence overall point being made by what you just read? What are the main pieces of information that feed into that overall point?
This process will give you practice with two things:
(1) Identifying "big picture" information vs. detailed information—and understanding when you need to pay more attention to understand the big picture vs. when you can just say to yourself, "Oh, that's some detail that I don't need right now."
(2) Summarizing information in your own words as you go. The more you understand the big picture of what you've already read, the more you can add in new information to make the overall story more rich / complex.
Here are some good sources for this kind of reading:
Free: University of Chicago Magazinemake_clickable_callback(MAGIC_URL_FULL, ' ', 'https://mag.uchicago.edu/', '', ' class="postlink"') Especially the Topics "Economics & Business," "Law, Policy & Society," and "Science & Medicine"
Free: MIT Open Coursewaremake_clickable_callback(MAGIC_URL_FULL, ' ', 'https://ocw.mit.edu/', '', ' class="postlink"') Pick any Undergraduate-level course and click on the Reading list for the course. Not everything will be freely available, but anything with a link is. Focus on introductory-level topics or articles within that course. (If you click on a Reading list and it has no links, just go find a different course.)
Paid: Harvard Business Review This is subscription-based, but they do have great articles.
When you go to any of those sources and choose an article, evaluate whether it's at the right level. If, during your first read, it seems too easy / lower-level compared to the GMAT, go find something else. Alternatively, if it seems too dense or technical for the GMAT, ditto, go find something else.
Try that and come back and tell us how it's going.