Tired of endlessly studying...

I had similar trouble breaking the 600 barrier some time back now im stuck with breaking the 650 barrier, but i can share my experience. The key is to review the break down of your mistakes and work specifically on those areas..

I was consistently scoring a 590, and i realized that i was making very specific mistakes eg. in CR and RC i had an issue with the inferenc question, i reviewed the basics and immediately saw my score jump... similarly i had issues with absolute value basics etc. in Quant and i practiced 700+ level problems and followed bunuel on the forum.. that will really help you gain a perspective on solving..

Stress management:
you need to be very very VERY wary of your state of mind while attempting the test, its all mere trickery and time management. I was able to consistently break the 600 barrier the moment i realised i was stressing unnecessarily on the exam. I was thinking about the type of questions, the amount of time i had spent on a question and probably gotten wrong etc. ALL unnecessary. The key is to focus on the one question that you are facing! and just aiming to hammer it into the ground the best you can. If you cant solve it in 2 minutes or even 3, rest assured its not meant to be, try to look at the options at hand take your pick and move on.

On time management:
you need to have a plan and strategy in mind when approaching the questions.. personally this is something i am still working on. while everyone says that the first few questions are the most important (and i do agree) you need to balance your time evenly. too much time spent early can result in a lot of random guessing at the end.. For this i have been repeatedly practicing on full sections managing my time on a 25:20:20:10 split on the quant (i am still perfecting this, so this isnt a golden rule and may not necessarily work for you!!)

Finally you need to tell yourself its just an exam, there are far more difficult things you may have done in your actual life, draw some inspiration from this and build your confidence!! (i ran a half marathon last weekend.. and i can tell you it is a tough one!!)

GO FOR GOLD!! and beat that GMAT!!