* Picasso96Mode resets the horizontal resolution from 1680 to 640 when I attempt to add a new mode to the board. Best I can do is 1600x1050 (currently running 1600x1200).
Have you tried to edit that 640 to 1680? I think the new mode tend always to start at 640x480 and then has to be edited to the desired but I'm not sure as many years gone since I last time created some.
Or try in small increments edit your mode larger to notice if some wall suddenly pops up.