The most common issue causing the people I work with and talk with to have trouble increasing their GMAT verbal scores is their doing most or all of their practice timed. When you cap the time per question you spend on verbal questions, you don't give yourself time to learn how to answer them correctly.
On the other hand, I have seen people's verbal scores increase substantially once they start doing practice questions untimed.
Why does practicing in that way work? For at least two reasons.
One reason is that, if you are really good at seeing what's going on in verbal questions, in most cases the time available per question will be practically irrelevant. You'll naturally answer them in less time per question than is allotted.
The second reason is that, by taking as much time as you need to correctly answer verbal questions, you go through the motions that you need to go through in order to do your job, which is to arrive at correct answers. Arriving at incorrect answers in under two minutes each is useless. You have to learn to see what you have to see and execute flawlessly.
You can be sure that, once you learn to see what you have to see and to execute well, you will naturally answer verbal questions in the time allotted. If you are having trouble answering them within the allotted time, you haven't become good enough at seeing what you have to see and at executing. The answer is not to use a stopwatch. The answer is to get better at seeing what you have to see and at executing.
Sure, some timed practice done close to when you are going to take the actual GMAT might make sense. Other than that, just take as much time as you need, and learn to get the questions correct.
By the way, if you want to score 770, your hit rate in when practicing has to be close to 100 percent. So, take as much time as you need per question to get 100 percent of your practice questions correct. Once you can consistently get, say, 50 correct in a row, look for ways to speed up. Can you read more efficiently? Can you better organize the way you go through the choices? Be strategic.