Certainly you can improve 120 points in 2 -3 months! Keep in mind that those are a tough 120 points to get from 590 to 710, but it can be done.
I am assuming that the 590 was on the actual test or an official GMATPrep practice. If so the good news is that you have the 89th percentile in verbal. When trying to achieve scores in the neighborhood of 700, the verbal score can be your best friend. I have written about this before and feel free to read some of my previous posts on the subject, but in brief it is because you only have to move up about 2 percent in the verbal to achieve a one point increase in your scaled score. Whereas above the 79th percentile in quant you need to move up about 4.5% to get a one point scaled score increase. So at 89 percentile in verbal you still have more than 5 points to be gained in verbal. So do not neglect the verbal. A high 99th percentile in verbal and a 74th in quant can give you a 99th overall.
That said, you will need to get the quant up to about the 60th to 70th percentile depending on how much you can improve your verbal score. If you are NOT trying to get to the 99th percentile in quant (and you may not be looking to get there) it will really help you to focus on getting a certain number of questions right on the test. You will miss questions, but if you find a way to get maybe 27 out of the 37 right on the quant. (in that range anyway) you should be able to achieve the kind of quant score you need to get a 710.
Also keep in mind that your score can vary on test day by up to 30 points from your "true score" based on factors like how many of the questions you miss are experimental.
But yes, you can get there.
By the way, in regards to your "cold turkey" test score being higher...it is not uncommon for scores to drop a little as students are taking in lots of new information, they know more so they try to do too much compared to when they had not studied. You score should improve as you integrate that information.
Good luck!
