trickiness preflop leads into a weird river c/r bluff w made hand

[luegofuego]

UTG (nitty reg playing 16/13, seems kinda weak and straightforward so far. $1,945 behind, i cover) opens for $75 utg. folded around to me in SB. i just call with K[img]/images/graemlins/diamond.gif[/img]K[img]/images/graemlins/club.gif[/img].

flop: J[img]/images/graemlins/diamond.gif[/img]Q[img]/images/graemlins/club.gif[/img]J[img]/images/graemlins/spade.gif[/img], i check and call $140

turn: 6[img]/images/graemlins/spade.gif[/img], i check, he checks.

river A[img]/images/graemlins/heart.gif[/img], i check, he tanks and bets $350. i raise everything... don't think he's seen me get horribly out of line and the only reason he might suspect i am capable is if he frequents 2+2.