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This is one of those situations in which calling/folding is completely turn and river dependant.

How LAGgy is the LAG? If he's something like 50/45 or 39/37, you should seriously consider check/mucking the flop even if you had top pair.

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Explain mucking a pair of Kings on this board.

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Note the bold in quotes.

Over a substantial number of hands, players with stats like that don't limp preflop. The small difference between VPIP and PFR is made up of:

95% from the blinds (completing SB and checking BB option)
5% from limping with AA or KK.