power steering problem

I recently replaced the power steering pump (with junkyard pump) on my 81 chevy 3/4 ton 4wd pickup. It has a 350 in it. So when i replaced it it was squealing really bad and was extremely hot. So was the steering box. In fact the metal part of the line where it connects to gearbox blistered me when i touched it. I spit on the gearbox and it sizzled the spit. Abnormally hot I thought, as I have changed these pumps before and never with this kind of heat, at least not that i remember. Since then (week ago) the pump just started doing it again. could this be something to do with the steering gearbox? Or do you think it's just bad luck with my choice for a junkyard pump? And why the heat? I shined a light in the pump with the truck running and it looks like fluid is circulating through the pump.

Thank you.