there is no setting for 4g. either data is on,or off,and the RIL/radio will determine if it wants to be on 3g,4g,etc.
4g dropping is a common result of bouncing around/changing firmwares after s-off. you need to reinstall the stock recovery and do a factory data reset,or clear storage, in hboot(no wiping data in amon recovery is not the same)
make a backup first,either option will factory reset your phone.