Bad PS pump, steering box, both?

[WestButteTruck]

It seems I have no power steering at lower rpm's trying to park, or turn while backing up, etc. At times I can't even turn the wheel at all until I give it some gas and go really easy on the wheel. And it will make a noisy sqeal sound too. No problems once I get going although I'm not turning sharp but you can still tell it has some drag on it. I know the gearbox is leaking some out the top. Is this a pump issue, or the gearbox? Fluid level is good when I have the problems. 83 Chevy 4x4, thanks