Yes, any time you flash a stock rom you have to re-root. What I did, if you search the dev section you can find Unleash the beast or even the old Superrooter Xtreme. I keep superrooter in a folder on my SD card. Any time I flash a stock rom, I go to MyFile and copy the superrooter update.zip to the root of my SD card, reboot into recovery, reinstall packages, and I'm rooter again. Then when done delete the update.zip from sd so I can load rom manager or whatever else.