Try the "2G/3G/Dual Mode Selection Applet" . Somebody probably set your phone for 3G operation, and since reflash, it has returned to default dual/2.5 preferred (dunno why, but the phone will never select 3G on this mode; mine won't, at least), but selecting the signal band thru the applet should fix that.

Personally, my phone has never selected a 3G network, but I never tested it, too. I'm currently in a non-3G area, but I'm going to a nearby city right now to buy a new keyboard, so I might as well test it there...

Btw, I'm not working here, too, lol.