I'm probably not qualified to comment here, but I think if you're going to limp-call with AK, you have to call him here. He may well have AQ or QQ or AA, but he could also have AJ or AT or AK or KK or something. He PFR'd and bet flop and turn when checked to on a drawy board against a limp-caller. To me, this doesn't need to show anything more than TPGK. How does he view your preflop play? If he sees you as "standard," he's probably putting you on a spade draw or JT for the double-gutter.