[Hocrest]

Your's sounds like a power issue. With the car running have someone
sit in it and turn the wheel back and forth while you stand in front and watch the PS pump pulley. If it "skips" at all then you need to tighten your belt. If it is already tight, it may be time for a new one.

Another thing that could cause slipping is a crank pulley that is beginning to separate. With some white-out, draw a line across all three sections of the pulley. After a period of slipping, look to see if the line is still a line.