i wouldnt worry about text books.
First get a solid base by reading kaplan a couple times (i took notes from the book while doing this to sink it in to my head).
Second, Start reading Cliff's AP Bio book to get everything STUCK in your head. I feel like reading textbooks would be beneficial, but in all honesty 32-34 of the 40 bio questions could be answered by using Kaplan, Cliffs, and Destroyer. For the other 6-8... theres just no way to prepare because the questions are such that they require you to link concepts together and reason. For OChem and GenChem, Destroyer and Kaplan will more than prepare you. If you are unsure of a subject, THEN look it up in a textbook or wiki.
Third, Use DAT DESTROYER to get used to answering problems. If you get a question wrong, understand why its wrong, and if you get it right, make sure you understand why its right.
After you have done all of the above, I would begin using the Topscore and Achiever Practice tests. These tests should not only be used as a gauge of your progress, but also as a study tool. Make sure you understand the concepts behing EVERY QUESTION. During this time, when you are not doing achiever or topscore tests, you should be reviewing the Cliffs book and kaplan book, and/or redoing all of the Destroyer problems.
For PAT and RC. Just PRACTICE PRACTICE PRACTICE. I used Crack DAT PAT for the PAT and it helped. I was getting 18's at first and got a 21 on the real deal.
If you do that then you will be set for success (I dont think you would get below a 19/19/19 at worst if you do this).
Hope this helps.
SM
