Hi Alok322,
While reading from outside sources certainly has the potential to help you hone your reading and 'retention' skills, you can't really train for the 'content' of the RC passages that you'll see on Test Day. The good news is that RC questions are more often about understanding the structure of the passage and why the passage was written than about understanding every word in the passage. In that way, you don't have to worry about the exact meaning of each sentence as long as you understand WHY the sentence is there (the role that it plays in that paragraph and in the larger passage). The types of RC questions that you'll see on Test Day are rather limited (and the wrong answers fall into predictable patterns as well), so in that way you CAN train to perform better on RC.
You mention having trouble concentrating on RC passages, but that is likely a different issue from actually having trouble with RC. Many Test Takers deal with significant fatigue and endurance issues in the Verbal section on Test Day (since that's the final 75 minutes of a 4-hour Exam and you don't begin that section until almost 3 hours have gone by). This is all meant to say that you should consider the Physical aspects of how you study and take your CATS (your posture, the amount of sleep that you get, what you eat/drink during your breaks, etc.).
1) How long have you studied?
2) What materials have you used?
3) How have you scored on each of your CATs (including the Quant and Verbal Scaled Scores)?
GMAT assassins aren't born, they're made,
Rich