Heads Up :
The post you are writing will appear in a public forum. Please ensure all content is appropriate for public consumption. Review the employee guidelines for the community here.
I started seeing the same problem after upgrading IOS, try using the 154-3 IOS images. You also might want to check into link-recovery or setting up a chat-script to send AT!RESET (this reboots the cellular modem itself only, not the hwic) or AT!GRE...