Hydrauilic assisted direction problem

The direction of my Chevrolet truck is super hard to turn to the sides they tell me that it is the hydraulic aciete pump but I do not know why apparently if the oil circulates.
We have done everything that a manual tells us to disagree at the exit to the pump, the pipe that enters the steering box and after which it leaves, the oil leaves but I do not have how to try the pressure and I continue with the problem that when I am going slowly or for parking it is super hard, it becomes completely mechanical and it is with hydraulic pump.

The pump may be oil but not enough to open the valve

This is also but you must also check the state of the oil and the pressure of the same, as well as the tension of the belt.

hello.
Your hydraulic or servoasistidal addresses?