Beach, I can empathize with you on the study techniques. I too find it hard to study for hours on end. What has helped me the most is targeting my studies. When I started studying for the DAT there were quite a number of areas in bio and ochem that I was just clueless on (like developmental bio and endocrinology). I focused hard on my weak areas (while studying in short intervals) and took practice tests regularly to gauge my progression, which has greatly improved.
Also, I think a large part of retaining information is repeated exposure to the material. Most people will not retain the numerous and minor details that this test requires by reading something once or twice.
Finally, you may consider condensing your study materials. For example, I have studied from the 'bluebook', and while it is extremely helpful, I find some of the material unnecessarily long. Condensing the information makes it easier to re-study the material; it also creates an more interaction while studying since you are thinking and writing about what you are studying. This helps me focus, since I am more engaged in the task.
Good luck!