I don't rule out the threat of a fullhouse.
K9/KT: he calls both preflop bets, bets flop but gets scared of the straight or better. Turn, makes the fullhouse and decides to do the delayed checkraise, hoping to trap both of you.
K3: Bets flop, but figured to slow down because of your aggression. Turn looks good, then river looks even better, decides to trap.

Seems weird for a donk to play the QJ, TT, or 99 that way though.