i'm assuming you're talking about gen chem..
note that this is just in my personal experience. i felt that kaplan is more than enough. i thought the practice questions were fair in difficulty for the most part, but when i got to the actual DAT, they were MUCH easier conceptually and in the amount of calculations needed. i was getting 18-19 in the kaplan and topscore gen chem sections, but got a 25 on the DAT.