Did you try a complete DFU reload without restoring from an iTunes backup and without PWNing it afterwards? That should put it back to stock software and configuration.
If that works, then do the other things one at a time (restoring, PWNing) and see when the WiFi fails. If it does it after restoring from backup (my guess), then something in your old config is corrupt. If nobody knows where to look (maybe a plist file someplace), then you're probably going to have to chuck the backup and start from scratch.
-- Nathan