The point of slowplaying is to give your opponent a chance to improve his hand to second best and try to make out that you did not hit the flop hard. After that flop, a diamond on the turn or a Q, J, T could improve his hand enough to beat you. Checking the flop might persuade him you are less likely to have an Ace, but as the next card is a King that does not help much. Bet out on the flop. If he folds, there was just no further money to be extracted on this hand.