different steering parts???

[Nukes16]

Does anyone know if there is a difference between the power steering pitman arm and the manual steering pitman arm, as well as the idler arms for both.
Also, there are 3 different power steering boxes listed in LMC for the specific years, do you know how/why they are different? Can I only use the one designated for my truck.... or are they interchangeable?
My steering problems are still here after I switched steering boxes, idler arms, checked my pitman arm and had it at the alignment shop. It is still overly twitchy and I'm constantly working the steering wheel. The only thing the alignment shop said was that the wheels are really difficult to turn when they are under load. I guess she comes apart once more!