After downloading the stock ROM, do this:
1) install the adb/fastboot files to a single directory onto your computer (I use the files from Myth Tools);
2) place the NON-HLOS.bin file in the adb/fastboot directory from step 1;
3) open a command prompt window as an administrator;
4) install the Motorola USB drivers and connect the booted phone with USB debugging enabled;
5) from the command line, type "adb reboot bootloader" and press the enter key to get my phone into AP Fastboot Flash mode;
6) from the command line, type "fastboot flash modem NON-HLOS.bin" and press enter; and
7) reboot the phone and check to made sure my baseband is correct.