Hi Harris,
(straight line) Seams should be as vertical or horizontal as possible in the UV Map, to avoid this kind of Aliasing/Pixelation.
Doesn’t explain the Pixel Size being too large though….
We have had a question here from someone with ‘the same’ problem and in that case, it turned out to be caused by Compositing Nodes, so I’d check that if I were you.
For the rest, it is really hard for me to troubleshoot. Hopefully someone else has a better idea as to what could be the issue.
