Ok, I pulled out my 1978 Argosy manual (mine is a '75 but they have the same chasis Chevy P30) and it recommends GM Power Steering Fluid or Dexron II Automatic Transmission fluid.
The more I read on here, and other places on the web, I think I'll try disconnecting all the lines and check for clogged or worn hoses and lines before I install the new pump. I bought a rebuilt one and it finally arrived today but I read on this post (see below) that a guy replaced 3 pumps before figuring out it was a clogged line that was causing his problem.
GM hydro-boost inop
Plus the instructions on replacing the pump call for all lines to be no older than 2 years old otherwise it voids the warranty. Probably just an easy out for them in case of failure but a good idea to check anyway.
I think your idea of using GM Power Steering fluid is wise. Since I'll more than likely drain just about the whole system disconnecting the lines I'll replace the fluid with the GM stuff.
Thanks again for your help.