Nandroid Backup. Wipe, factory reset, data and dalvik. Then install a rooted stock asop rom and try the update. Make sure you have the latest radio.
If it still doesn't connect, unroot your phone, uninstall rooted apps like SU and Terminal Editor, reset to stock and give it try. If that fails bring it to a Sprint tech, if they can't get it fixed they will offer another coarse of action.
Hope that helps. There are many threads about this on xda and other forums. I went through it too. Best of luck.