Punches do work the lats, so you're doing everything alright. For lower body, you might want to concentrate on the inward motion to see if that will help. When you kick out, try to bring your leg back into the bent leg position (the term for it eludes me for the moment) as fast as possible--as if you were kicking into fire, or as if your leg were like the tongue of a frog whipping out and back quickly. You should feel it more in the hamstrings then.