i know this sounds really lame and it may sound like a bit of overkill, but adcoms say that rc and bio are the most important sections so i figured why not... i am a very slow reader too, so i went to the library and got sat book, gmat, lsat, and mcat books and i am doing all of the rc/va sections in those books... i have the exam crackers 101 passages and i am almost finished with that as well... just so that you know, it is really helpful because they are different types of reading, but still they are timed and will give you a good feel for the time constraint... what i find most helpful in increasing my reading efficiancy (which is the most important thing) is doing the old school mcat exams (prior to the cbt), there were 60 questions in 85 min... it gets you used to something more strenuous (geez my spelling is horrific... dont judge) and it forces you to get used to that vs. the dat which is 60 min (not a walk in the park, but those extra 25 min really get you)
hope this helps...