Did you update to ipad baseband ? If you have, then custom firmware of 4.2.1 is the way to go or if you have 4.1 blob, you can actually restore to stock 4.1
Ok, i will give you the cfw of 4.2.1 . rename .zip to .ipsw and run redsn0w 0.9.6b6 , browse to stock 4.2.1 fw and check only the box dfu mode only.
Run itunes and restore to this file ( in your PM box)
You have to run redsnow to install cydia again.