Very unlikely that your PS pump is bad. Those Saginaw pumps are old-fashioned as an anvil and every bit as durable. Lots of these trucks go to the boneyard with 400k+ miles with their original PS pump still installed. The only exception to that is if you've ever had a leak in the system and the pump was run dry. Does it make any noise or have any roughness in rotation when you turn it by hand?Ok had the belts off started her up and …………..no noises
put the belts back on and ……….no noises
Turned her off and checked it over,there is a very slight ply in the power steering pulley.Could it be the pumps on its way out?