The ordeals of an oil man!!!

Profile: Indian, M25, Mechanical engineering Degree with a GPA of 3.0
WE: 0.5 years in a manufacturing plant (irrelevant); 3.5+ years in an Indian Upstream oil company, out of which 2+ years as a driller and 1.5 yrs as a drilling engineer
Target schools: ISB, NUS, NTU
EC : average

I started my preparation several times in the last 2 years and each of those never lasted for more than a week!! But i became serious in the last 2-3 months and started devoting a few hours every day.

Preparation materials: Manhattan SC book, Powerscore CR, OG 12, and random questions posted in Gmatclub
I am extremely thankful to bunuel,his explanations were really helpful during my preparation.

Practice test scores:
Gmatprep 1- 590 (before prep) ,
Gmatprep II - 690(10 days before the test)
Manhattan scores were from 660 to 720. The 720(q 48, v40) was on cat6 taken 2 days before the actual exam. I went for the exam with a target score of 730-740 with 49 in quant and 40 in verbal.

Gmat experience: The AWA was alright-not my best, but hopefully should still fetch around 4.5-5. In IR, my plan was to skip the 3 multisource reasoning questions as those questions were time consuming in the Gmatprep and mgmat cat tests. In the real test, the first 3 questions were multi source reasoning questions, but it looked pretty simple. So i just skipped through the passage and answered/ guessed those 3 and moved on in 3 minutes. But this was a huge mistake as a second batch of 3 multisource questions appeared as questions 8-10. This second batch of MS questions were way too tough and i was not able to figure anything out even after spending around 8 minutes. So i had to guess and move on. Other IR questions were easy. So i am still hopeful of getting a 5 in IR.

Quant went very easy and at the end of the session i was sure of getting atleast a 50. There were a few tricky questions, but i was well on time throughout and i felt very comfortable compared to the mgmat tests which used to make me feel exhausted by the end of 75 minutes.

Since i was happy with my performance in quant, i was very confident when i started my verbal session. But it did not last long, the first few questions were SC and they just blew me away. Seriously, the verbal part in the real exam was tougher than the mgmat or gmatprep tests. After around 20 questions i understood that i was well behind my timing plan. So i was nervous and this put me in real trouble. I had around one minute each for the last 13 questions, so it was really getting tougher towards the end. Somehow i managed to finish the exam and i was really really disappointed with my performance.

Final score: 690 (Q46, v38)
When i clicked the calculate score button, i was expecting a score of q50, v35(or may be even less) to come up. But to my big surprise, it was the other way around. The score showed that i did a decent job in verbal, whereas something had terribly gone wrong in quant. Even after 10 days from the test, i still do not know where i went wrong in quant. I was particularly careful in DS questions and spent some time to recheck my answers before i pressed next button.

Anyway, i have decided to retake Gmat within a month. I clearly know what i have to do for verbal-concentrate more on timing, especially in CR. But i am still pondering on how to improve my quant. Though i am an engineer, i am not a math whiz. But i am not too bad either. In almost all the practice tests, i had scored around 48-49. I never neglected quant. Infact, i was more confident in verbal while going for the final exam. I am really looking for some advice on how to improve my quant, especially from people who have faced similar situation.