I just killed the root on my spare d4 after the JB update and used the Razr Blade root with no problems. However it does use SuperSU so you would want to remove the superuser after rooting and not have both. You can get it here: http://www.droidrzr.com/index.php/topic/6924-root-achieved-for-jb-ota-razrmaxx-xt912/ or Dev-Host - razr_blade.zip - The Ultimate Free File Hosting / File Sharing Service. Be sure to unzip it before running.