How did you reflash back to stock? Did you flash the official Google images or restore a nandroid? I would suggest reverting to the stock images and trying again.
Can you verify the SIM is working properly with the APN you are using in another device?
Current Personal Phone: Google Nexus 4 on Cricket/Aio (Beanstalk
4.4.4 with hells-Core Kernel
Current Work Phone: LG G2 VS980 on VZW (Official Beanstalk
Current Tablet: iPad 4 and Samsung Galaxy Note Pro 12.2
Other phones "in the family": HTC DNA, HTC One (M7), Motorola Moto G GPE
Previous/Retired Android Devices: HTC Aria, HTC Incredible 2, HTC Rezound, Samsung Stratosphere, Samsung Galaxy S2 Skyrocket, Nextbook 8P