1. get the
original SPL for your phone, go to the SPL thread at the top
2. rename it to update.zip and flash it to your phone
3. download the DREAIMG.nbh from the thread where you rooted your phone
4. place DREAIMG.nbh on the root of your SD card and start phone in bootloader(camera+power)
5. hit power to start the update DO NOT INTERRUPT!! i can not stress this enough
6. hit action(trackball down) and your phone will reboot
7. YOU NOW HAVE STOCK FIRMWARE, it will update on it's own in a little bit
the above is from the xda-forums.