To truly unroot you first need to flash the "Unevoked S-On" tool. It can be found on unrevoked's site, xda_developers.com, ppcgeeks.com, etc. Search for it. Once you have that file, place it on the root directory of your sd card and flash it like a custom Rom. After that you can then use you pc/laptop to run the stock Sprint ruu which Can be downloaded at shipped-roms.com.