Honestly, I just changed the way I've been reading the passages...you don't need to understand what every single sentence means - like you said, if you understand the point of the passage you can get pretty much every question right. At the end of each paragraph, I summarize in my head what the "point" of that paragraph is, and then at the end i ask myself (literally) "why did the author write this?" The only time I don't do this is when I get a natural sciences passage, for those I try to understand every detail because questions can be specific.
On a related note, I very rarely go back to read the passage while trying to answer a question. I think sometimes you can have an idea what the right answer is, but going back to the passage can really distract you from choosing the right answer. I predict what I think the answer will be in my head and then just go with my gut in picking the answer closest to that.
Lastly, if I don't know the answer after 30 or so seconds of thought, I pick one and move on. If you don't know the answer after 30 seconds of thought, you probably wont know it after 2 minutes. Last year I was always tight on time and it was because I spent too much time on the questions i was unsure of.
I've seen these strategies posted a bunch of bunch of times, but it wasn't until I actively started trying them that my scores improved...hope some of this helps