Hi cheryn.
Regarding reading slowly versus reading fast, what I've found is that you have to read slowly enough to understand what the passage is saying, but you don't have to get every detail down when you are reading the passage. What you have to do is NOTE WHERE THE DETAILS LIE so that you can go back and find them as necessary when answering questions.
That said, when you are PRACTICING, at first, you should take as much time as you need per question to get the questions correct close to 100 percent of the time. You have to practice untimed to learn to do the main thing that you have to do, which is arrive at correct answers. Take ten minutes per question if necessary, and learn to see what you have to see and be precise enough in your thinking to arrive at a correct answer almost every time.
THEN, once you are skilled at arriving at correct answers, seek to speed up while still arriving at correct answers.
Remember, all the information needed to answer the questions is right there in the passage. So, the key to correcty answering an RC question is determining what the passage says and what it DOES NOT say and, thus, arrive at the correct answer rather than be tricked into choosing a trap answer based on something that the passage doesn't say.