I was going to say what Laura said, which is treat RC like LR questions. Someone else said this, and it's really true. Even some of the questions are exact LR questions, though I wouldn't say they are all similar to Must Be True.
I did a Testmasters weekend course and as someone said with Powerscore, we didn't spend that much time on RC but what we did do was helpful. Some of this might seem obvious, but it wasn't for me and can help increase speed. Our tutor suggested numbering all the paragraphs. Again, this might seem obvious, but can help accumulate a wee bit of time when they say things like 'in paragraph 4'. You can jump right in because you know where it is. He also suggested writing a word or two beside each paragraph to describe what it's about. I try and write as little as possible but usually for me this is a small phrase. Not only is it helpful for referring back to the passage, it also helps in your mind summing up a paragraph. What is this author saying right here. And can help with questions that ask what the passage as whole is trying to do.
I agree with whoever said that RC hasn't really gotten harder. I find that comparative reading is actually the easiest section of RC, and in my (albeit) small prep class, pretty much everyone got 5/6 or 6/7 right in that section. I agree with the idea of looking at perhaps a dense article and then trying to identify the MP, author's attitude etc. Again, people have given tips for this but author's attitude is all in the words and nuances. As I said in another thread, as soon as I saw the word 'draconian' i circled it. It's such a strong and interesting word to use, there was a reason for it. Anything that gives a suggestion of tone, I mark or make note of in some way.
As for articles to read, I wouldn't really suggest The Economist since it's such a conversational magazine, I would probably recommend something like Foreign Affairs or as Laura suggested, even a bad piece of writing. Perhaps Tatler or something of that ilk. Again, as Laura said, groupthink was a difficult passage to grasp as a whole (esp. if you were low on time which I was coming off of cakewalk) and on the Princeton Review site, when Groupthink was part of the experimental section, they said the best way to handle it was actually to diagram some of the stuff.
I was also getting -1 or -2 on my PT's in the RC section near the end of my study, and got a -7 on the June test in that section. It was all in group think and at the bottom of cakewalk. As soon as I became pressed for time, there were issues in thinking clearly.
Kind of makes me think of when I was 8 or so and competing in my first proper skating tournament and had been practicing and doing really well at my program. Then when it was my time to perform, I started off strong and about 15 seconds in, realized I was behind the time and by quite a bit, so I skipped the whole rest of the routine to end on time