Let me start by saying that you should buy any and every book that you want to and I would never want to discourage you. I am just saying that this is a lot of work in a long book that is based on a different test.
* Remember that on the LSAT you have 28 questions in just 35 minutes. Not much more than 1 minute per question. Whereas on the GMAT you have 2 minutes per question.
* On the LSAT you know how many questions per passage and you can move around and answer them in a different order.
* The LSAT is on paper and you can mark things up as you read it. The GMAT is not.
* Other differences that do not occur to me at this moment!
I am not saying that LSAT questions are not good to study. I am saying that your APPROACH needs to be GMAT-specific.
Now, It is certainly true that there are more specific questions than general questions.
Let me ask you this? HOW do you usually begin a specific question? If you say "that you go from the question stem to the answer choices" that may be part of your problem. Process of Elimination is a nice tool for many things on the GMAT - but this is not the way to begin these specific questions.
When you are asked a specific question you can always return to the passage!! It is right there for you. Countless people have been helped on reading comprehension tremendously just be understanding that it is quicker to go back to the passage rather than to begin with process of elimination.
You have scared me very much when you say that the book is going to teach you to "read minute details effectively." When you are reading you are not looking to memorize or write down the minute details. You are not even really supposed to pay too much attention to them. I think this is what you meant when you said that so we are on the same page there.
If the passage says that 1,729,893 people died in World War 1 and 4,374,893 people died in World War 2 (I made these numbers up I have no notion of the real totals)...anyway all you would think is "more died in World War 2." If you need to get more specific you can do that WHEN they ask the question.
Try this...after you have read the passage and written down the MAIN IDEA of each paragraph (split really long paragraphs in two)...when you get to a question ask yourself if you can go back to a specific paragraph based on the question stem. If you can it is usually best to do so. Allow the question stem to guide you to the part to re-read. once you have re-read you will find that the correct answer is a paraphrase of that portion of the text.
Try it!