Default [Q] Switching Carriers

I have an odd problem. I got my Nexus 5 on launch week and had been using it on At&t for the first month. In December I decided to try switching to Metro PCS to get unlimited LTE. For some reason I couldn't get any signal. I would get signal for about a half hour once a week. I gave up on that and stayed on ATT. In January, I tried doing the T-Mobile $30 prepaid with 100 min + unl text/web but I couldn't get signal either. I did full wipes each time but I seem to only be able to get any service with ATT now. Has anyone tried and successfully switched carriers with the same nexus or is it just mine that's acting up?