Hey,
I took the DAT twice, got 17 on reading the first time, and 21 the second time. The reading is pretty variable and it also depends on your own performance on the test day. I would say the Crack DAT reading comes closest to whats on the actual test. The reading on topscore doesn't have many tone or inference questions which could pop up on the exam. DAT achiever will really push you to the limit if you want something challenging.
If you don't get the reading score you want, the thing that helped me improve the 2nd time was reading novels that were interesting to me such as Kite Runner, Memoirs of a Geisha, etc. Keep doing practice tests from topscore and whatever programs you find helpful.
Cheers