Right, so I'm from Whitby and we've got our own big cat sightings on the North York Moors going back decades, and the pattern you're describing matches almost exactly what gets reported over here - large, black, low-slung silhouette, moves too smooth to be a dog, vanishes before you can get a proper look.
The thing that always gets me with these sightings is how consistent the witness descriptions are across completely different continents. Nobody's coordinating thier stories. A farmer outside Asheville and a hiker on the moors are not comparing notes, yet they're seeing the same thing.
Has anyone managed to get track casts or anything physical from the Asheville area? Over here the best evidence tends to come from livestock attacks where the kill pattern doesn't match any known local predator. Worth checking with local farmers if any of them have had unusual losses they've written off as coyote kills.