Drop the transmission oil pan and look for metal fragments. If anything nasty was going wrong in the trans you'll find debris, plus the GTR trans is pretty sensitive to throwing CEL codes when things start to go wrong.
I still think diff bind to be honest. Why it happens going from 2nd to 3rd, who knows. There could be other factors at play, not necessarily related to the gear change from 2nd to 3rd, and turning right.
IMO I would start thinking about getting Martin's 2009/2010 refresh kit done. Once my '10 is out of warranty, its the first thing I'll be doing.
I'm in no way an expert in all of this, Martin is surely the man to ask/confirm. However I've read enough horror storys on NAGTROC to have a fair idea.
Also on the positive side, the fact that you've done 50 something thousand kms in yours without issues is simply amazing and gives me hope!!!!!