I had a very similar hand yesterday. I played it the same way as you but I really hated being capped on the turn. Villains hand at showdown shocked me as well.

Ultimate Bet 0.50/1 Hold'em (8 handed) converter

Preflop: Hero is MP2 with A[img]/images/graemlins/club.gif[/img], A[img]/images/graemlins/heart.gif[/img].
<font color="#666666">3 folds</font>, <font color="#CC3333">Hero raises</font>, <font color="#666666">2 folds</font>, SB calls, <font color="#666666">1 fold</font>.

Flop: (5 SB) 6[img]/images/graemlins/heart.gif[/img], J[img]/images/graemlins/heart.gif[/img], 5[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(2 players)</font>
SB checks, <font color="#CC3333">Hero bets</font>, SB calls.

Turn: (3.50 BB) K[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(2 players)</font>
SB checks, <font color="#CC3333">Hero bets</font>, <font color="#CC3333">SB raises</font>, <font color="#CC3333">Hero 3-bets</font>, <font color="#CC3333">SB caps</font>, Hero calls.

River: (11.50 BB) 5[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">SB bets</font>, Hero calls.

Final Pot: 13.50 BB

Results in white below: <font color="#FFFFFF">
SB has Kh Kd (full house, kings full of fives).
Hero has Ac Ah (two pair, aces and fives).
Outcome: SB wins 13.50 BB. </font>