My guess is that the pies were underdone. I doubt the dome was anywhere near 750F if the stone was only 550F. It would be hard to get that much of a differential without insulation. Maybe, but even at those temps, 2 minutes doesn't seem like enough time. When I was baking on my grill at 750F on Fibrament and well above that in the dome via lots of insulation, the fastest time I could get was 2:15 or so.
Are you baking on the Baking Steel or a stone? If a stone, what sort of stone?