3G, 2G and phone not working - 4g works

I'm having a somewhat odd issue with my Nexus 5. 4G connects fine and I can use all of the internet things, but if I put the phone in 3G or 2G only, it completely loses service. Switch it back to 4G, it connects again. If I try to make a phone call, it drops the call and shows no service again, even though 4G is enabled and was working when I initiated the call. Does anyone have any ideas what could be causing that? I tried calling T-Mobile, LG and Google support and the best thing they could say is to factory reset or send it in. Before I called them, I had already tried every image for it on Google's site and Cyanogenmod, so I'm pretty sure it's not a software issue. Anyone have any ideas what else I may be able to try or maybe something that would need to be replaced? I have no problem taking it apart if I need to.