James,
Your post is timely; I'm battling through the same issue, actually. I've been working on my grip for quite some time now -- at least since late last summer, really -- still trying to find the correct positioning of the left hand.
The problem I'm experiencing is, at impact, my left pinky finger fails to hold on to the grip tight enough; the middle two fingers do hold on, though and touch my palm at address. Post impact, the grip loosens, and the clubface closes. Over time, I've subconsciously over-compensated for this by adjusting setup, grip and alignment incorrectly. The left hand really is that important, I've determined.
I'm doing simple drills now to address the issue and strengthen my grip: gripping the club, and extending it out away from my body, and parallel to the ground to ensure it's square to target at address. Otherwise, I'm at a loss for what to do, which is why I've turned here.
For what it's worth, I did a good amount of research on
human anthropometry (the measurements and proportion of anatomy) and found that, over all, I have a larger hand (80th percentile of adult men) with a large palm (90th percentile) and small fingers (30-40 percentile). Now, my hands are not oddities -- they appear normal -- its just the component pieces are different, i.e., I'm "human".
Help.