At this point I have not had any luck solving this issue. I used Guru's reset tool as well and believe the problem is the radio firmware. I spent a good deal of time on the phone with Sprint support and with a surprisingly competent technician in the store. He tried to work with multiple different systems they have available to get the phone to recognize the Sprint towers with no success.
He said that the phone just isn't recognizing them in any way and commented that a phone that isn't activated will still show bars of service because the phone gets the signals from nearby towers, but just doesn't know what to do with the signal until activated. In my case, all I see is the "X" above the signal bar graphic.
If you're experiencing the same issue as me, there is nothing Sprint can do to make the phone recognize their towers based on the conversations I've had. I saw my options as:
1. Wait for an RUU to come out or something like that
2. Try out different ROMs - jjmckaskie suggested the newest CM, but I would think others might be worth trying as well. Basically anything that uses different radio firmware
3. Get a new phone - This is the option I've gone with. Since my phone is running a stock ROM and the guy at Best Buy where my insurance is from, didn't check the bootloader (would have said "tampered" and "unlocked"), he assumed I never voided my warranty and sent out for a refurb. This may not work if your insurance is through Sprint though. I'm not sure how thorough they are.