Not 100% if it's the same on the Sierra but did you examine the cup that the tripod joint fits into? I had these breaking on me all the time in my Focus and i discovered that i'd worn a groove on the inside of the cup which was caused by the vibration - but that caused the replacement item to fail quicker because there was more play in it from the off.

Just a though, would hate to see you do all the work and have it fail again.