Welcome to the forum.
If I had to guess, I would say that the problem is the use of the Pampered Chef stone on the lowest oven rack position.
I am not personally familiar with the Pampered Chef stone, but I see them offered all the time at eBay, and at prices that are a fraction of the prices of other pizza stones intended for serious home pizza makers. From the photos of the Pampered Chef stones I have seen, they look to be quite thin, maybe as thin as a quarter-inch or half-inch. The largest size (diameter) Pampered Chef stone I have seen is 15 inches. If I am correct on this, the mass of such a stone will be quite small compared with most other pizza stones and placing such a stone in close proximity to the oven's lower heating element will cause it to heat up very quickly and achieve a temperature that is considerably higher than the ambient air above the stone that bakes the top of the pizza. Under these conditions, it is easy for the bottom of the crust to burn and turn black. The problem will be even more severe if your stone is less than 15 inches in diameter, because of its even lower mass. If the problem arose after you moved the stone to the lowest oven rack position, that would seem to suggest that the problem is with the stone and its positioning in the oven.
I suggest that you try using the middle oven rack position for your stone to see if the problem goes away. If the problem reoccurs, then you might move the stone another level up in your oven and see if that helps. Another possible solution is to use the middle oven rack position and lower the oven temperature to say, 450-475 degrees F. This will mean a longer bake time, but the pizza crust should bake properly both top and bottom and produce a crust that is crispy and with good texture, flavor and color. Tom Lehmann himself often recommends using lower bake temperatures and longer bake times.
If it turns out that your pizza stone is hampering instead of pampering your pizza making skills, you might want to consider a more substantial pizza stone or even a set of tiles. The tiles are thin, but there are usually several of them and, collectively, they provide sufficient mass and surface area to do an effective job, even at the lowest oven rack position.
The only other thing that I can think of as a possible cause of the problem you experienced is if you used sugar in your Lehmann dough recipe. Tom Lehmann usually does not recommend sugar in the dough if the pizza is to be baked on a hearth type surface at high temperatures because the sugar caramelizes too quickly and the bottom crust can brown, and even burn, before the rest of the pizza is finished baking. If you used sugar in the Lehmann recipe you selected, then I would recommend that you try deleting it next time to see if it is the cause or a contributing factor to the problem you have recently been experiencing.
I'm confident that you will in due course be able to overcome your present problem and be able to make some good pizzas, whether the Lehmann NY style or otherwise.