Why does my new S3 only show 3G and not 4G? My S2 show 4G in the same location, so my location shouldn't be the issue. The S3 doesn't even have a "4G on/off" setting in the settings menu - that I've found.
Your 4G on your Galaxy S2 is based on Wimax technology. That is now a legacy technology because they are switching to LTE. So where your area was a Wimax area, sprint has not rolled out 4g LTE yet.
Don't worry though, when LTE is up, you will not miss wimax at all. Wimax speeds are typically 5-9 megs per second. On my Verizon LTE I get as much as 31 megs per second in NYC. People out in the sticks gets as high as 60+ megs per second. Its is not even close to be honest with you.
By default, it's set to 3G. You can turn on 4G, but that will be useless if you're not in a 4G area.
If you turn on 4G, and you're not in a 4G, it will show 3G, but if you slip into an area with 4G, it will automatically pick up the4G signal and display it.
I have mine set to 4G for the hell of it, and there is no noticeable battery drain, although some people have said otherwise.