I did some further research. The slop in the tone pot is about 1/2 a number in both directions. For example, if you turn up from 8 to 9, it goes to 8-1/2 before any resistance, and sound does not change until that point. Turning down from 5 to 4, the knob goes to 4-1/2 before any resistance, and sound does not change until that point. The guitar is playable, but the slop is kind of annoying, especially in a brand new instrument.
I checked the mounting nut on the pot with a thin wrench (11mm from a bicycle kit). The nut was tight. With the knob pulled up, you can see the shaft rotate with the knob, so the knob is tight. The slop is apparently inside the pot.
Also noticed that the tone changes gradually throughout the rotation, but changes suddenly when 0 is reached. I assume that is because the pot is taken out of the circuit at that point.
I contacted the dealer, who said that the slop is "totally normal". Could it be a push-pull knob characteristic? I do not have another guitar with push-pull knobs to compare, but none of my other guitars have any slop at all in any of the knobs.
It is not feasible to take the guitar back to the dealer since his shop is a 3-hour drive away. Might try to contact PRS directly to see if they have any recommendations.