99 Malibu hard steering question

Hi all,

I have a 99 malibu with a 3.1. The steering is very difficult when backing out of a parking space etc both to the left and right. The weird thing is that it starts out ok in the morning and gets worse in short order( a few minutes). It seems to steer fine during normal driving speeds.
I just replaced the serpentine belt and all pulleys are good. I also cleaned all the pulleys before installing the new belt.The PS pump does not whine and there are no visible bubbles. Fluid level is good.

While sitting, if I slowly turn the wheel until it starts to get hard to turn then hold slight tension on it I can hit the gas while its in neutral and the wheel will "break free" and turn fine. In other words, power assist seems to work fine at high RPMs.

If it was the pump wouldn't it be hard to steer all the time?

I'm out of ideas accept for the steering rack. But why does it start out OK?

A very experienced mechanic told me it may be the strut towers are siezed. I have never put struts on this thing and it has 160K.

If anybody can help me out with this I'd appreciate it. I don't want to try a new pump for the sake of part swapping.

Thanks

Well, it is usually either the gearbox or the pump, I would think. Don't see how the struts would impact this unless the front struts are "binding".