GMAT Strategy

I took the GMAT first time in February last year. I worked with all 3 OG guides + online Kaplan material. I studied for 4month. I scored 490.... (Verbal 21 /Quantitative36) I took several GMAT prepsoftware test and always scored the range between 430 and 500..... At that time I was more worried in quantity than in quality. My math bases were not the best. I Then I came to this site and found several advices.
I decided to first work in my Math basis. I first made a guide of basic math that had nothing to do with GMAT but that covered all the basis (fractions, number prop, etc….). Then I made all the Manhattan GMAT guides 2007 (excluding the critical reasoning, geometry and I just read the theory of the reading comprehension guide but I did not do any exercise). I did the entire CR bible and I did the entire orange OG guide excluding the RC… On the RC instead I read every day 3 hr of books in english). I timed every time I practiced for both quant and verbal. I studied for 5 month. I took just 1 test prepsoftware test one week before the test and scored 590 (Quant 44 / verbal 21). Because I just need 550 I decided to take the test and score a pathetic 450(Quant37/ Verbal 17). I think I was nervous but not to blame my nerves for this score.
I am going to take the test again in 1 ½ month. I need your advices because I do not know what else to do. I consider that my weakness areas are: RC and CR (Verbal in general). In the Quant I feel now more secure and even though I do not know why I did not increased my Quant score I feel that this is not the area of the problem. I run out of time in the last 8 questions for every both Quant and Verbal).

Please help because I do not know what else to do.

Hello Erick;
Thanks a lot for helping me to understand what I am doing wrong.
My target score is just 600, but I can be accepted in the program of my choice with 550.
During my preparation I used an excel grid analyzing my errors. I also repeated all the problems I got wrong until get them right. I organized my study plan with the input of all those post (Ursula's Strategy, TwinnSplitter's Strategy) including yours.
My weakness is verbal and maybe one of my errors is that I just took 1 mock before the test. I think that this time I should take several full length test to build my stamina.
One of the issues that I have seen that happen with me is that if for example I decide to make again the CR Bible, I know the theory and I understand it… But when I am going to apply the theory is when I do not see the results……Maybe I need more practice with the OG material forcing my self to practice using the strategies learned. Likewise is SC… If I decide to go over again with the Manhattan SC…I will see that I know the theory and I understand it… but when I am going to solve a problem is not so obvious to apply it.
What do you think about this???.... What do you recommend me?