I had the same problem, but fixed it last night. I backed up using iTunes, did a complete reset, all settings, all data, deleted everything, and registered as new iPad. Then restored from iTunes.
It worked, I have had 3G service for the last 24 hours.
The restore didn't work perfectly, some photos disappeared, as did some apps, but the photos were backed up, and when I downloaded the missing apps they came back with usernames and settings intact.
So, all is good with it now. My iPad (2 32Gb GSM) is now faster, about the same as with IOS 7.