I have experienced the squealing come from power steering pump and from the pulleys. Different times similiar squeal.
Difference in sound was the bad pulley/belt issue was more like you described at the higher RPM's. This had a higher thinner pitch. The power steering pump was heavier metal to metal sound....hope that didnt sound crazy.
Each time the parts were replaced the sound went away. The other thing is confirm the size of the belts you used to replace yours. If you had upgraded pulleys then you might need a different size from original belts.
Look under my old post on the power steering pump for some help. Good luck.