I have tried but never been able to understand saying "I have been constantly scoring in GMAT-Prep this much ..." There are only two CATs - you can score two times on two CATs. How it's possible for one to score constantly within the certain ranges and consider this as pillar. I am not pointing even the fact, that many if not all GMAT-Prep questions are posted through numerous forums and may be found in the diff. prep company materials. If you have your baseline score before studying GMAT at certain level and then study to increase this score, it doesn't mean that the score should be increasing ... Anyways, I believe your problem lies with verbal section and this part of test should be approached gradually or with very systematic and focused training program. You cannot score 28 and then retake test for scoring 40+ just because your focus was impaired. There are certain blocks of knowledge tested in verbal

As mentioned in the previous reply, verbal seems to have played an important role in your result. Irrespective of the GMAPPrep score you have observed, have you done OG end to end for SC and CR?

Also it helps to get the Error tracker from BTG and understand where you are making most errors in SC. Manhattan SC helped me a lot with increasing my accuracy. In verbal, it helps to start actively reading the content from leading business publishers like Economist, Wall Street Journal and Financial Times. If not in SC, this beyond the GMAT prep reading helps in CR and AWA.

When you scored higher in the prep tests, have you also finished AWA??, since doing end to end keeps the realistic tab on the stamina.