deadly alignment?

[fastlane]

I've got a 69 c10 2wd. I've had it aligned twice now, and it is undrivable at highway speeds. Both places want to blame the steering box (brand new redhead box [also a manual to p/s conversion]) I can see a bit of touchiness due to a possible to much pressure from the pump situation. but from one exit to the next I was fearful of my life and those around me. every bump I hit I was recovering for 2-300 yards. Also with NO input from the steering wheel it would dart slightly within the lane. this thing is scary! All steering components are new (tie rods, ball joints, control arm bushings, etc.) Please help.