The priority valve makes sure you have steering before anything else,so that could be your problem,follow your hydraulic lines it should leave the pump and go to the inlet of the loader valve, out of the loader valve to the priority valve, from the priority valve to the steering box and to the rear 3-point.You may need to get a gauge to confirm whats going on.I'm assuming your tractor has 1- hydraulic pump for everything
Tommy
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