steering is very stiff and the fluid is ok

I just went through this in my jeep, it is your power steering pump, if your fluid is topped off, put your car on a very leveled surface. Have some body that's strong turning the wheel completely left to right, have them keep doing this while you watch for any fluid movement in the reservoir, if the isn't any movement beyond the car moving from the turning of the wheel then fluid isn't being pumped

P.s don't top off the fluid, just make sure it's at fill level when cold