As I have stated in a previous post, this is how the settings break down:
CDMA Auto: Any 2G/3G connection based upon PRL (preferred roaming list)
CDMA only: Only 2G (1xRTT) connection. Expect slow data speeds.
EV-DO only: Only 3G (EV-DO) connection. Expect voice/SMS issues.
CDMA + LTE/EV-DO Auto: Uses any 2G/3G/4G connection. Default setting.
Set this to either CDMA Auto or CDMA + LTE/EV-DO Auto unless attempting the 1xRTT fix for downloading the OTA update.
The only way to reliably disable the 4G while keeping all other services is to set it to CDMA Auto.