Can't lock onto GPS. Flash/Root possibly related
It sounds to me like the flashing wiped out all the info your phone had about local satellites -- the good stuff it retrieves itself, not the aGPS crap :P. If that's the case then hopefully this will help; this a process I've used on my Samsung Vibrant.


Ensure GPS is disabled
Go to LbsTestMode
Hit Delete GPS Data
Go into Application Settings
Change Start Mode to Cold start
Back out to the home screen, then reboot your phone
Enable GPS
Go to LbsTestMode
Hit Get Position Test.  Let this run to completion (normally a good 15 minutes or so) &mdash; the lat/long info will get filled in and you'll see [*] next to several of the satellites it finds, the more the better.  This will work best if you go outside and walk around.
Back out and go into Application Settings again.
Change Start Mode back to Hot start.
Reboot and, hopefully, enjoy your functional GPS.