Thanks to Noemi for remaining present in this forum. I'm more than happy to wait out the break-in period, and I will let you know if I need assistance in the future. So far, my dealership has been accommodating and reassuring, so we'll see.
That said, the question that remains, for me, is the following: has anyone who's had the "my car intermittently sounds and feels like there's gravel in the transmission" found that the (putative) problem resolves after the 1000-mile break-in period? It seems that there's a rather broad severity range... Any thoughts would be welcome, as I'm trying to find some grounds for having confidence in the car at the moment.