When turning left the power steering makes a whine/squeal noise?

Hello. My power steering is starting to whine/squeal when turning left. The steering fluid seems full when hot. The belt seems to be very tight.

Also, randomly the voltage will drop to about 12. And when that happens. It seems to slightly loose a little bit of steering power with it. Almost not noticeable. But when I turn the truck off and back on it works for a while again.

Too tight of belt? Pump just going out? Help please and thank you.