HI Geoff, I stumbled around with your excellent advice and just couldn't make anything happen. I did a factory reset and installed AOKP build 4 and boom it worked. It only connects on LTE Only but I wasn't complaining.
I cut through Charlestown, Somerville and through Fresh Pond rotary to Rt 2 west. Had coverage the whole trip until 128, the LTE went cold. I updated sensorly. Not sure where the tower is near Mass Ave and Alewife Parkway but the signal was really strong. I got 17 down and 8 up. Not too shabby.