go into stock recovery and factory reset.
Then after booting up shut down completely.
Then boot to recovery.
Reflash the .tar (follow previous proceedure)
And see if the baseband/modem is properly updated this time.
I read that some people, after taking the latest OTA (the same as the .tar) have had to go back to sprint to have them fix it - most likely just flashing the modem.
That being said since there are some (read many) people having this issue with NC6, you can always try to Odin the NAF .tar
and see if all works.
Then if you want
try and take the Sprint OTA (via system settings>more>updates and check there.