Greg, your shoes could still be the culprit, even though you loosened the straps a bit on your last ride, they might be too narrow in the toe area or not have enough padding in the insole to protect the bottom of your foot. If that were the case, I would think you would feel some discomfort prior to getting a "tingling/foot going to sleep" feeling.
I tend to get that tingly toe feeling a bit when I'm working hard over several miles and I have found that my shoes/pedals/socks have nothing to do with it.
I tend to get my seat bones in a position that I think pinches some nerves, or something, that causes that "going to sleep feeling" in my toes and balls of my feet.
All I have to do is ride out of the sadle for 30 seconds or so, and the feeling starts to go away. Then I remind myself that even though I'm pedaling hard, I need to concentrate on being relaxed, getting tensed up doesn't help a bit.
Anyway, I still think you need to get to the point where you can ride a couple of hours comfortably, and that may be at a slow pace. That'll tell you whether your clothing (shoes) and bike fit is correct.
Then when you start working for power/speed you'll know the only variable that has changed is how hard you're mashing the pedals.