I found a solution to downgrade the iOS on my iPad from 4.3b3 to 4.2.1*I had IOS 4.3b3 on it. what I did was to upgrade to 4.2.1. Upgrade with shift+upgrade and used orginal iOS 4.2.1. You wil get an error in iTunes ignore it. Use tinyumbrella to kick it out of recovery it will start normal and ask for unlock kode ignore it. then i run Greenpos0n RC5_2. and you have IPad on iOS 4.2.1 jailbreaked
Just do a iTunes shift+restore and select iOS 4.2.1. you wil get error 1015 ignore it. just run Grenposi0n RC5 and you ar on 4.2.1 jailbreaked YES!!