Restore and see if that fixes it. (If it doesn't, call apple but dont tell them you jailbroke it.) Then try jailbreaking again. Sometimes not everything works first time...
I've jailbroken my Iphone 4 4.1 with both Limera1n and Greenpois0n and have the same problem. My GPS is always searching, it jumps around but never gets my position. :/ It works when not jailbroken..
Same here. My sat nav wouldn't pick up a signal at all. Sat nav is a must for me but it didn't want to work for me when my phone was on tethered JB, so I just gave up and will wait for untethered. It worked fine when I was on 4.1 untethered...oh man do I miss 4.1.;-((