I recently bought a Samsung Galaxy S III. I know it is 100% compatible with AT&T's 4G LTE network (it was made for this). AT&T offers 4G service in my area. I'm not getting speeds any faster than the 3G+ speeds I was before. Is this a setting I can get changed? I even bought a brand new SIM card so it would work correctly out of the box

Thank you,
DmT