If you zoom in further, does it still appear misaligned? If so, I think it's your vertices that are the problem, they must be slightly out of line. If they shimmer in and out of alignment, it could be a display issue. I'd bet on it being the vertices themselves.
Just pack your uvs as a rectangle vertically in 0-1, work away as normal, export 4k maps, resize/crop in PS. Or unwrap vertically across 2 uv tiles and scale uniformly into half of 0-1.