Hey Ann, I think you have a problem of being results-oriented. I think your blaming of first instinct is somewhat of a cop-out. Let me try to explain before sounding like a jerk.
I bet when you go over your tests and review the questions, you realize that you missed a lot of questions when you knew the info/content. It seems like you attribute your mistakes to your first instinct, but neglect the fact that you got some questions right solely because of your first instinct. Most people are like this and make the error of convincing themselves that all the questions they got right were a result of understanding everything. I think its just the way people are. When we are super seriously intensely debating between 2 possible answer choices, we end up marking 1 answer, and when we find out later that we missed it because we tricked ourselves. This makes us feel like we sort of knew the answer/content. On the flip side, when we are in the same situation and get the question right, we tend to attribute that correct response to our superior ability to reason.
My point to all of this is that you have to really try and be honest with yourself about what you were thinking during the test. It doesn't mean anything if your practice test score is high, but got the right answers through incorrect logic. I've never heard of a med school asking what you got on practice tests. Find out why your first instincts are the way they are, because I bet the deeper problem can be traced to a lack of content understanding. These test makers purposefully put in answer choices that are designed to trap students and trick them into making fundamental errors. Strong content understanding is required to avoid such pitfalls. I think you should try to put in more effort to eliminating incorrect answers before immediately looking for the right one.