Why are you changing them?
I've worked on these trucks for a long time and only ever replaced two steering boxes. One probably could have been fixed (set preload) but the customer wanted a new one swapped in.
As for pumps, I've only ever replaced them for leaking, and I had one that the shaft was broken off in.
Make sure if there's any mechanical failure in the system you flush it really well. If the pump exploded (ie: there's metal filings in the fluid) the only REAL way to get all the **** out of the HOSES is replace them - the metallic debris is like glass, it will imbed in the hoses and cause ALLLLL kinds of grief.
Hope this is of some help to you, post let me know what the repeat issue is!