@n80, the way to strengthen your left hand is to lead with it. If you are practicing rudiments (do it on a practice pad, rather than sitting at your set), play the "R" parts with your left hand, the "L" with your right. Set your kit up backwards, forcing yourself to play left handed and footed. It will feel very awkward and you'll suck at it, but it will bring your left hand and foot closer to your right. Did you know that although Ringo set-up and played right handed, on his fills he led with his left hand? Weird!