first of all i would take every test timed, because the combination of speed and precision is what nets 170s. . .also you are right in spacing out the preptests - they are valuable commodities because they come with official explanations! what you should do is examine the preptest explanation for every missed question and write down in a journal what your thought process should have been leading into the question in order to have answered it correctly, thus "downloading" the correct "program" into your brain the next time a similar question arises.