OK, let's reason this out--new pump, new fluid, plenty of time (running time) to "burp" the system of air. Assuming the hoses are connected, that only leaves one element with uncertain health--THE STEERING BOX.
On GM-type integral power assist steering gear boxes, there is a spool valve that must slide when torque is applied to the steering wheel shaft. This spool valve then ports PS fluid to the proper side of the power pistol, which pushes on the ball nut, which in turn rotates the sector shaft, which is connected to the pitman arm.
I would bet your spool valve is stuck with some crap (dirt, metal chips, etc.) that is keeping it from porting the fluid correctly. (I say this assuming you don't feel and "tight" or "binding" spots in the steering, just a lack of power assist.)
If my assumption is correct, it's new steering gear time. Best/cheapest bet here is the boneyard. Rebuilding a Saginaw (GM) box is out of the league of most of us without special tools.