Based on the amount of wrenching you are doing yourself, I'm going to assume you know what you are doing... but just incase... I figure I might post anyway.
You are priming the turbos with oil before you install them right? You need to make sure they have some oil in them, otherwise on the very first startup they spin with dry bearings (or bushings)... it's enough to scar the shaft and cause permanent damage.
I'm assuming you know that much, so otherwise I'm going to guess it was just a bad batch.