Staying focused requires you to really do some silly things - pretend that this is the most important thing you've ever read; read with an enthusiastic voice; pretend you're the author and arguing your point with someone who disagrees with you. Any way you can get "into" the passage regardless of the subject. As for mapping, it does take time to write things out, so mental mapping is best. After each paragraph, summarize quickly what the arguments were.... as you read, expand and build on that, especially paying attention to the key phrases or repetitive ideas. If you need more than that, judiciously using the highlighter tool for key phrases / repetitive elements might be a help.

For practice material, the Khan academy passages are the closest to the AAMC logic and reasoning.

Hope that helps!

Meaghan.