The only reason to check Kxx in a 3bet pot as the reraiser is if we know villain will bet when we check, and is unlikely to fold to later bets. On occasion, we can exploit villain tendencies, but it's important to have a solid read on villain to take unusual lines. Very few villains will meet this criteria, so don't make assumptions. Just bet Kxx and Axx when we 3bet and get called, regardless of whether we have the nuts or pure garbage.