You are still at the early stage of your preparation, so speed should not be a major concern for you right now. The main problem is probably familiarity with the concepts. Solid guidebooks correct this problem. And that's what you should focus on at this time: study guides and some OG to reinforce the concepts.
One good idea is to consider any problem that takes more than two minutes incorrect during question practice sessions. This allows you to revisit those questions later.
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