[cleszkie]

What is the ratio on a stock steering box? Perhaps your new box and the other one you tried out are making the steering too "twitchy" (small movement of steering wheel results in big movement of wheels). If that is the case, you will have a hard time keeping the steering wheel still enough to maintain a straight line down the road. I had this issue on another truck of mine. Totally undriveable until I replaced the steering box with a "slower" one that required a lot more movement of the steering wheel to turn the wheels.

Regarding your hydroboost system, I think I recall replacing my stock flow control valve on my pump with a special valve that was provided in the hydroboost kit I bought. I don't know if the replacement valve was needed in order provide the correct hose fitting, or if it actualyy modified the flow for use in a hydroboost system.