I have to guess 3-4 questions on average as I run out of time all the time (since I am in the higher range, most of the questions I get are 700+ and some of them have been really gruelling and time consuming).. so I am left with no choice but to skip them entirely..
This happens for everybody, regardless of your scoring level or how much you study. You can't avoid having to make some guesses. All you can do is choose when (on which questions) you want to guess. You never want to guess on 3-4 questions in a row because, out of any 3-4 questions in a row, some of those questions are ones you can do. Therefore, you want to choose the hardest 3-4 questions as you see them throughout the test. Make your guesses on those, not the last 3-4 in a row.
Although I did not time myself while practicing through these books and may well have gone beyond stipulated 2 mins/per question (RC and CR)
If that's actually the case, then your percentage correct doesn't matter. The test is not merely asking how many you can get right; it's asking how many you can get right in the very limited time available. That's a completely different question. As noted above for quant, you're going to have to guess sometimes, so choose the hardest ones as you find them. (Most people have to guess on 4-7 per section unless their score is at the higher end, when it might drop to 3 or 4.)
usually the tough maths section drains away most of my brain power and focus and leaves me with very little during the verbal
This may get a bit better if you use the strategy I described above - when you see the hardest quant questions, let them go. (It doesn't hurt your score to get the hardest ones wrong - but it does hurt your score if you get a few wrong in a row at the end because you ran out of time and had to make random guesses.)
I have not been writing essays in any of the mocks
This, however, is the bigger issue with why you get tired our during the verbal. You've only prepared yourself fora 2.5 hour test. The test is actually 3.5 hours, and that last hour (for which you're not prepared) is all verbal!
There's not a lot you can do now, 2 days before the test, to develop this mental stamina. If you postpone or take the test again in future, make sure to do the essays every time. I know you don't really care about the essay score, but you do care about the verbal score - and that can be negatively affected if you haven't been practicing with the essays!
If most of your recent tests have been around the 650 range, then that's what you should expect on the real test - and possibly a little bit lower, because you haven't been doing the essays (skipping the essays can inflate your score sometimes). If you really want a 700+, then you may want to postpone this test date until your practice test scores (with the essays, under all official timing conditions) are in the 700 range.