Default Virgin Mobile Galaxy S III on CM11 M8 LTE issues

Hello. I apologize if I'm in the wrong place, I'm new to the forum. I'm having an issue with my 4G LTE. Whatever I do I cant seem to get my 4G working. The best I can do is get 3G. Can someone either tell me how to fix this or link me to a fix? I've been looking every where but I can't find anything definitive! I have a Galaxy S 3 L710 under virgin mobile. Thanks!