2004 Highlander power steering help

Wifes car is starting to get hard to steer in the morning or when the car sits over night. When she tries to move in the morning the wheel is sticking not moving easily/hard steering. It will do this until it warms up or she revs the engine up. Just a fast minutes worth and car is good for the day. Would this be the start of the power steering pump going or the rack n pinion going? I know its hard to answer but I'm leaning towards the power steering pump. Is the power steering pump hard to change considering its way down on the bottom firewall side? Any suggestions? Thanks.

A lot of GM cars used to have this problem some years ago, the racks had to be replaced. I have heard that sometimes flushing out the old power steering fluid sometimes works.