If you are on EI22 and rooted, frequent reboots happen. Also Sprint is going to relentlessly try to OTA you over to EL30 after you reboot. But the OTA won't work on a rooted EI22 rom.
Check here:
Epic 4G Android Development - xda-developers
And find yourself an EL30 rom to flash. You'll also have to flash or odin the EL30 modem. Or you can dl and then odin the whole stock EL30 package here:
[EL30] Official EL30 Stock Tar w/modem! SPH-D700-EL30-8Gb-REL.tar.md5 - xda-developers
But you'll have to re-root and reinstall CWM afterwrds.