Well, I feel stupid.
Last night I decided to take a little closer look at the situation. As it turns out, the kitchen vent was closed most of the way! I could have sworn it was open. I know I've felt heat comming out of it before. Anyway, in my defense, it has a brass decorative cover over it, and the flapper part is black and behind the brass cover so its really hard to see. Its open now and I should have a good deal more heat in the kitchen. We'll see how that works!