He is 39/13 over 96 hands. I am the Button with KsQc.

Do I snap call this river bet when I hit my straight? Thought on the whole hand.

You hit your straight and there are only 3 hands you're afraid of: JT/44/99.

Hands you beat: QQ-AA, AT, KT, AJ, KJ, QJ.

If you're one of those math guys you can run the equity calculation and see what you get. Or you can get a feel for how likely it is that he has one of the few hands that beat you vs. one of the hands you beat.

Personally I'm also afraid of JJ and TT

I surely wouldn't snap-call river. Massive overbet is either the nuts hoping you hit that T or something or it's air... (Unless you think villain would do this with AA, can't imagine though. You call 2 streets so villain should be thinking about you having the T as well, or another proper hand.)

Then again, with a good hand you'd want to build a pot. Of course villain could also have the exact same hand you have.

I could see myself raising turn sometimes. Repping the T or boat, but having a redraw if getting called. Should be able to get the right villain to fold quite some hands.

BUt that might be the exact reason I'm actually loosing on 10NL

I think that you're afraid of the following hands:
TT, JJ, 44, JT, T9, 99

The only two pair hand that he can have is J9 (discounting hands like J4 or 94).
No way he has a worse straight (78 wouldn't bet the flop and turn like this).
There's no FD on the board.
It's hard to believe that he would take top or middle pair this far (hands like AJ, AT, KT, KJ) on a board that is so connected with an opponent calling down all of his bets.

He may be bluffing but is it worth your stack to find out?

It's a tough spot and it's definitely not a snap call in my opinion. After 96 hands with him, you may have a feel for whether he is getting out of line with top pair or whether he is bluffing. If you have no read on him, I would fold.

Given there's no busted flush draw, I think this kind of shove is more likely a boat. Without any other reads I think its a fold. Don't know whether I actually could in game tho

Big bet preflop: pairs, AJ+, KQ heavier on his range.

Small half pot twice on Flop and Turn: he either connected strong and want to build the pot or is drawing for the straight.

Big Bet River: he built the pot and now he is being greedy or he connected the straight.

I can only see you ahead if he has ATs. He can have the same straight as you. Or he is ahead with TT, JJ.
The bet is too big to call.

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