I thnk *#06* is showing IMEI properly ...
" 357537...245 / 01 "
If IMEI is showing properly there shouldnt be any problem in running 3G :S. That's one strange problem you got there.
OK Found this on XDA. i think it might help. Try this And report back.
Downgrade to 4.2.2, And do the following.
Dial *#0808#; select RNDIS - DM - Modem and apply
Install qpst on PC and their drivers;
Open Qpst config; add port, select diagnostic com port, then download EFS Professional
open it and click qualcomm nv tools, open it select com port and then connect,
go to third tab, tick IMEI(DEC) and write your given IMEI at the back of the Galaxy S4 (found in your profile) and then click write and reboot
you have your IMEI, after then flash stock 4.4.2