The day will never come when you can walk into a room and command respect simply because of your title or position. Respect must always be earned.
Consider the President of the United States. Half the country disdains him. The other half thinks they could do some things better.
So what makes you think that getting a promotion - becoming a manager - also grants with it some sort of commanded respect? Now, those who report to you might provide you with some sort of reverent deference - but only because you possess firing privileges over them. We must not confuse that kind of quasi-fear with genuine respect.
To get that, you must earn it. Every time. And with every person.