On your last hand, he sounds like he had JJ and wanted to be 100% sure you had him beat. $3 UTG with KK sounds about right. $5 on the flop looks good. The minraise would worry me, so I would probably call from that point on and look for a cheap finish. The all-in is a risky but effective way to end a hand, though: you probably have the best hand and you do get SOME better hands to fold SOME of the time - you also get SOME weaker hands to call SOME of the time.