Has anyone seen or experienced this? For lack of the proper word I will call it the steering gear box knuckle. The knuckle sheared/broke in half luckily while in a parking lot and not going down the freeway at 70mph. Common or not so common?

 

The part you are referring to is called the sector shaft.
I have never seen one of these break, but it could be a casting defect or possibly due to what we call shock loading. Have you had this vehicle from new? If not, unknown what the previous owner may have hit with it. Can you post some close up pix of the actual break surfaces if they are reasonably clean? Fractures can reveal a lot .

 

I've seen a few break, and some that have twisted the splines like a barber pole but haven't broken yet.

Like Hanky mention, if something was hit hard (especially if the steering was allowed to slam against the the spindle steering stops) it will twist the shaft and cause a failure point. Pay special attention to the remaining spline area, if they look twisted at all it was an impact caused failure. I used to do a lot of commercial SD fleet work and never been witness to a 'normal break' unless the shaft was stressed to the point of failure. Or close too..

 

I purchased the truck in 2001 with 41000 miles on it. Had a 6" suspension lift installed in 2003. Had 35" BFG's since then until last year when I went to 37's. In my possession it has never been off road. Currently as the truck sits it only has 168,000 miles on it. The picture posted was the only one I took. Will stop by the dealer and see if I can take a few more pics. It has been sitting there since 8/1. Thanks for the replies.