Thanks for the ideas!

I only know of one difference between the 95-99 gears and the 00-01 5
speed gears: slightly modified oil grooving.  Perhaps they improved the
material a little bit, I dunno.  The shafts are definitely the same.  I
haven't rebuilt enough of the 00-01's to determine if they were built
properly, but the couple I've done were correct.

One well-regarded internet source found that when he redid his diff
bearings that he needed a different set of bearing shims.  Assuming his
housings hadn't warped, his postulation that the factory set endplay
wrong is a valid one.

But I think it goes beyond that.  My experience rebuilding 95-99 5
speeds has resulted in a large pile of diff bearing shims in just 3
sizes.  I've never found any other shim size in a stock tranny, although
when I rebuild them the shim sizes I use end up all over the tolerance
range.  (There are over a dozen shim sizes).  My hypothesis, which will
never be known for sure, is that the original tranny builders did not
have the full range of shim sizes onhand to accurately set the diff
bearing endplay.  So if you were lucky your tranny required the shim
sizes that were on hand.  If you were unlucky your tranny needed a much
different shim size and it left the factory with incorrect endplay
setting, doomed to die a premature death.  Some trannys died within the
factory warranty, but most lasted just long enough to die out of
warranty and within the car's typical life.

Most rebuilders will just re-use the shims and not remeasure.  They
aren't aware of this endplay setting problem, because most trannys are
built right in the first place.  Most customers don't want to wait the
extra days to get the correct shim size from Nissan, and it will easily
outlast the 6 month or 12 month rebuilders warranty.  I always measure
until I'm confident I have the endplay within .001", and use the exact
recommended shim size.  To avoid delays I keep almost every shim size on
hand.  (this is only viable because I rebuild 95-01 trannys almost
exclusively)

Dave