Cold Weather make me have to pump brakes

Hey Guys, and gals,
So I have a 95 Rodeo 4x4. When it's cold (below 30 degrees) I have to pump the brakes to soften them up. Otherwise, it feels like I have
no power brakes at all. It takes about 3 pumps to get them going. Has anyone else had this experience? I'm wondering if it is the check valve.

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