Heater Control Box
 

The middle blue lever is relatively tough to move back and forth, the other 2 are fine. Any tips on how to best (most easily) improve the movement?

Spray some penatrating oil on the cable (under dash and in trunk) it'll soak in after a while and should free things up.

Also make sure the cables are fastened properly in the trunk. It's pretty easy to tell if the clamps have fallen off or are loose by pulling off the cover (in the trunk) and eyeballing things while someone else moves the lever.