6-7 degrees warmer upstairs, duct work problem, or insulation problem?

I'm trying to figure out why our master bedroom, which is on the top floor is so hard to cool!! The vent pushing in cold air is strong upstairs, and the return vent is weak!... It does cool, but the downstairs has to be an icebox! Also, it's only an issue when it's not terribly hot out, when the a/c... show more I'm trying to figure out why our master bedroom, which is on the top floor is so hard to cool!! The vent pushing in cold air is strong upstairs, and the return vent is weak!... It does cool, but the downstairs has to be an icebox!
Also, it's only an issue when it's not terribly hot out, when the a/c doesn't have to work hard, it eventually becomes only 3-4 degrees warmer upstairs

The house is from 1940's, has r-11-19 insulation in the attic, and in winter the heat doesn't rise, it's the same as the bottom floor, so I guess that's a sign of attic insulation needed??

But I DON'T want insulation to help warm the upstairs in winter, I like it cool upstairs in winter! It's the summer heat upstairs I can't stand!!

Should I start with getting insulation estimates, or looking at the return air vent? I don't know which I should start with! And like I said, I don't care about insulation helping heat the house in winter, all I care about is cooling it in summer! The ceiling fan does help mix the air but it doesn't fix the problem.

Insulation, or return duct? Thanks in advance
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