Don't give up!
Also, I find that doing lower body weight training (GS Legs, for exammple), makes all my cardio workouts better. After just a couple of weeks of doing GS Legs once a week makes my aerobic workouts leaps and bounds more efficient! I really notice this in Lowmax when I'm doing the kicking sequences. My kicks are sharper, crisper, and more controlled since I've been doing GS Legs once a week.
I think you'll find the same to be true of core work, too, when it comes to KPC. In other words, the stronger your core is, the better you'll be at KPC, since the core is engaged so much in this workout.