I river trips vs a nit...and check/fold?

[deaders]

This guy was pretty nitty 18/12/1.5 only cbets 50%, we dont have any real history but my image is aggressive tag, 25/20ish at the time.

Full Tilt Poker, $1/$2 NL Hold'em Cash Game, 5 Players
LeggoPoker.com - Hand History Converter

BTN: $105.05
Hero (SB): $208.95
BB: $101.30
UTG: $287.35
CO: $106.65

Pre-Flop: 8[img]/images/graemlins/diamond.gif[/img] A[img]/images/graemlins/diamond.gif[/img] dealt to Hero (SB)
<font color="red">UTG raises to $8</font>, CO calls $8, BTN folds, Hero calls $7, BB folds

Flop: ($26) 4[img]/images/graemlins/heart.gif[/img] 9[img]/images/graemlins/diamond.gif[/img] 8[img]/images/graemlins/club.gif[/img] (3 Players)
Hero checks, UTG checks, CO checks

Turn: ($26) T[img]/images/graemlins/diamond.gif[/img] (3 Players)
<font color="red">Hero bets $18</font>, <font color="red">UTG raises to $45</font>, CO folds, Hero calls $27

River: ($116) 8[img]/images/graemlins/heart.gif[/img] (2 Players)
Hero checks, <font color="red">UTG bets $66</font>

Preflop... meh CO and BB were both huge fish so I didnt mind seeing a multiway pot with them. Calling the turn raise seems standard yeah? His range for checking the flop then raising the turn must be pretty narrow, I havent seen him do anything to indicate that he could do it with air - he could possibly check sets on the flop because hes obviously not that great a player, and QJ is in there as well.