Another thing to try might be to take notes. Not so much about what is said but about the structure of the passage, so that you know the overall gist of things and where you can find different information. Even something as simple as
will help you get the main idea and understand where in the passage to go back to specific detail. I also find that writing things down keeps me more engaged in my reading.
If you are looking for more difficult RC questions, you might want to look into LSAT questions. The LSAT passages are the very similar to 600+level GMAT RC questions and passages.