I found that my problem was unclear instruction about the timing between jumping and popping. One day when I was watching a slowmo ollie video though, I noticed that the skateboarder already was beginning to jump (at least his body was already going in an upward motion) before snapping the board off the ground. That was a critical change I needed to make in order to get it working. I had been trying to pop the board while all my weight was still pushing down on it (kind of an obvious mistake, but I somehow overlooked this). Hope this helps somebody.
To get higher ollies, I would suggesting resting your back foot on the very end of the tail and the front foot in the middle of the deck to allow for more slide. Popping as hard as you can and catching your board in the groove of the nose with you ankle practically resting in the groove will level the board out in the air. after this initial movement slide you feet back to the bolts on the tail and nose to ensure a clean landing.