Power steering problem, need some help

[Chevlowrider]

Ive got a 1997 C1500 truck with a 5.3 from an 02 silverado. Im running the stock steering gear box in the truck and the stock power steering pump on the 5.3. at low rpm I loose power steering. I thought maybe it had something to do with the 5.3 pump not pumping enough for the gear box at low rpm so I put a pulley from a 3.4 car on it and still no change. Could it be a bad power steering pump? Its full on fluid, and i dont think there is any air in the system and no foaming in the resevoir. Any help would be awesome, thanks!

[93GMC]

Might be worth replacing the pump... no squeaking or whining ?

[Chevlowrider]

Might be worth replacing the pump... no squeaking or whining ?

At first no but after driving it for a little while it starts to whine

[kewljay223]

i had my lines reversed and it whined at higher speed. but there was also foaming though unlike yours. id double check your lines and if that isnt it, then id throw a new pump on.