[KHALI]

I think villians hand range in this situation is large as this could easily be a value type raise(sweetener like JTsuited) with a weird suited connector all the way up to big hand. Could narrow it down versus tight player but unknown???
I think that every street but the flop was played strangely enough to create doubt and I would call almost all the time here knowing I am probably beat. As other poster said a river check raise is rarely bluff but in this case it could be a strange desperation move to get you to fold in big pot.
I would also bet this river without much hesitation.

This hand reminds of a hand from Harrington's first book where an innocent looking card hits on river and villian wakes up. He says there is enough doubt to call. I will try to find page number.
Then again turn check call looks like a hand looking for help on river. Can't see pocket 6's not getting more bets in on turn with draws out there but is villian is maniacish could he have played a very strange 67suited or even A8,A6suited? Interested in result. But I call to see for sure. Rambling.