Is it be beneficial to quit job and start preparing for gate preparation.

Dear Amit
Basically, you've more experience than us. But just take it as suggestion. If you're fully fed up with job and really interested and having that confidence to clear the Gate exam. Then you can resign your job and you can join any best coaching center. Here you need to think about your family perspective too.
All the best. Take the wise decision.

It also depends which type of job you are doing. If you want to score good in GATE & with job you are unable to maintain the time for your study. Then it would be better to quit the job & do start your preparation.