To start with, don't take practice tests so frequently.
Practice tests are to test whether you have learned all the things you wanted to learn between the last practice test and the next one. Taking the test itself is not where the major learning comes from.
(And fluctuations are not unusual - your score would fluctuate quite a bit even if you'd been taking real tests. These types of tests are nowhere near as precise as everybody assumes they are.)
Generally speaking, I'd say tests every 3 weeks (approx.) until you get to within about a month of the real test. Then a test one month before, two weeks before and one week before, ideally at the same time of day as you plan to take the official test.
Part of what you'll need to do is see whether RC is slowing you down - are you taking too much time also or is it just that you're getting the harder ones wrong? You have to do somewhat different things to get better at timing vs. accuracy (though they're also interrelated obviously).
I assume you have already used some resource that talks about how to read the passages in order to extract the most useful information without getting too bogged down in the details and losing time? If you haven't, some ideas are below, but you should also ask around here and get something - there are a lot of books from GMAT companies that address this.
What is the purpose / main idea of each individual paragraph?
What kind of info is contained in the various paragraphs?
- background info / context
- support for the main point / purpose (this is generally the largest category of info)
- the actual main point / purpose
- follow-on discussion / expounding upon the main point / purpose
Is there any foreshadowing that gives you an idea of what's coming?
RC Questions:
Is it a general question or a specific one?
If general, what type?
- main idea
- passage structure
- tone
If specific, what type?
- specific detail, what
- specific detail, why
- inference
(those three are the main types, though there are other minor types)
Do you know how to handle each of those types? Do you know what they want? (This is different for each type.)
Also, start analyzing those answer choices. Here are some ideas to get you started.
RWP: Real World Plausible. The info sounds good in the real world, but I'm supposed to limit myself only to what the passage tells me.
DC: The info is directly contradicted by the passage
The Mix-Up: Two different pieces of info from the passage have been mashed together in a way that is not what the passage actually says - it just looks good b/c the two different pieces are discussed (separately) in the passage
Extreme: extreme words -- always, never -- typically indicate wrong answers (on RC - this is not as certain on CR)
TBNR: True But Not Right. This info is actually presented just as stated in the passage... but it doesn't answer the question that was just asked.
And, of course, the biggest category of all: Out of Scope. (RWP is a subset of OOS.) The info goes beyond what the passage actually says and we can't do that.
