Stiff brake pedal

The benefits of drum brakes are that there is little to no drag in their resting state.

Make sure they turn freely. When car is on jack stands, they should spin with little to no drag.

If no drag then refer to post #2

If rod is correct then I like to give em a good bleed.

If problem persists after bleeding then consider the master isn’t correct.

When it’s up on stands take pictures and measure drums.

Post pictures of shoe orientation and innards as well as master cylinder for best results.

If the proportioning valve looks new, please include pictures of that.

I bet someone will spot your issue.

This will be the fastest way.

$0.02