Question on Borgenson power steering box

I installed a Borgenson steering box kit from this sites vender. Everything was great and installed easily. I used my original 1967 273 power steering pump. The steering feels a little stiff untill the engine reaches 12 to 1400 rpm. Does this power steering box work better with more pressure? would a new pump help? Can a smaller pulley be used on the pump to help. Am I on the wrong track? Thoughts? I appreciate any help guys.

Donald