get the 2x format zip and run that in custom recovery before you wipe and do a clean install.
alternatively when you factory reset, clear /data, /cache etc stuff manually twice.
I have yet to look into whether or how to do a low-level format on this phone (or if it's even necessary on flash devices-- perhaps the controller just marks off problematic blocks as it encounters them), but in the past I have improved SDcard reliability with a low level format marking off the bad sectors.