Power Steering

I have been having issues with losing power steering at or slightly above idle. My pump is also making a whining noise like a pump does when it is low on fluid, however mine is full. I just found out there may be a filter in line for this system. Any suggestions on repairs? I am deciding to either rebuild the unit or replace with a reman unit. I have read that when replacing, this is when the filter should be changed. It is an inline filter and I do not see one. Could my filter be plugged or is this a common problem for Fords?