Mike,
Like many of us on the forum who make pizzas only occasionally and in small numbers and, hence, haven't developed great expertise in opening up dough balls to form skins of uniform thickness, you may just need more practice. This is a common problem, even among pizza operators who have to train their workers, as noted at this PMQ Think Tank thread:
http://www.pmq.com/tt/viewtopic.php?p=40908#40908.
You might want to try the tip recommended by Tom Lehmann in his post in the above thread but use a rolling pin instead of a sheeter to form skins part way until you become more proficient at forming full size skins entirely by hand. Another possibility is to use a lower hydration, say, 58%. Skins at that hydration value should be easier to work with and to get a more consistent and uniform skin thickness. Once you feel more comfortable with handling the skins at that hydration level, you can gradually increase the hydration stepwise until you are able to find the sweet spot for you from a handling standpoint.
Peter