Was I right to slow down on the river?

[Solovon]

Flopped trips, turned a full house, but with the action I thought it was definitely possible that someone's two pair had turned into queens full, so I decided to call down the river after the turn got capped. Was this right or can I keep betting this river for value in this massive pot?

PokerStars 0.50/1.00 Hold'em (5 handed) converter

Preflop: Hero is BB with 6[img]/images/graemlins/spade.gif[/img], 6[img]/images/graemlins/club.gif[/img].
UTG calls, <font color="#666666">1 fold</font>, Button calls, SB completes, Hero checks.

Flop: (4 SB) Q[img]/images/graemlins/diamond.gif[/img], 7[img]/images/graemlins/heart.gif[/img], 6[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(4 players)</font>
<font color="#CC3333">SB bets</font>, Hero calls, <font color="#CC3333">UTG raises</font>, <font color="#CC3333">Button 3-bets</font>, SB calls, <font color="#CC3333">Hero caps</font>, UTG calls, Button calls, SB calls.

Turn: (10 BB) Q[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(4 players)</font>
SB checks, <font color="#CC3333">Hero bets</font>, <font color="#CC3333">UTG raises</font>, Button calls, SB calls, <font color="#CC3333">Hero 3-bets</font>, <font color="#CC3333">UTG caps</font>, Button calls, SB calls, Hero calls.

River: (26 BB) 8[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(4 players)</font>
SB checks, Hero checks, <font color="#CC3333">UTG bets</font>, Button calls, SB folds, Hero calls.

Final Pot: 29 BB