Are you 100% sure you're in a 3G area?
/b
I had this same problem. My Blackberry would show strong 3g connection but my iPad would show little to no signal. I had talked to my carrier (using Rogers here in .CA) and they did not know what to tell me! Talked to Apple and they walked me through several steps. I ended up doing a complete restore to factory settings as suggested by Apple.
In the end I walked into an Apple store with it and (even though I purchased online) and talked to my 'Genius' and he ended up replacing it. My NEW iPad works great! It turns out that I had a DUD all along.
They didn't replace it with one from a retail box. The replacement models are brand new, but come in a 'mail back' box. I couldn't have been happier!
Not sure if this helps...
I've had a somewhat? similar issue that I haven't seen anywhere here., I jb too, and unless I activated 3G and maybe even left 3G antenna turned on BEFORE I jb, I could never get 3G service after I jb, only Edge.
but once I reset all to factory, made sure 3G was on, and then jb I always get 3G fine. If I did not do this, I always only got edge.
It was odd. works perfectly but only if I do the set up as indicated. I haven't found anyone else having this issue.
I had had a genius appointment after tech at Apple and ATT could not get 3G connecting, after lots of resets etc. later I starting toubleshooting myself, then I unjailbroke, reformatted and 3G worked fine. I cancelled my appt seeing as it was related to the jb. then I just turned on 3G first, it all works fine.