Default Low LTE signal after screen replacement

So I busted my S4's screen in Busan a little over two months ago and I just got around to replacing it (I'm back in the states now). However, my LTE signal is unusually low now, it sits at about 1 or 2 bars, or shows none at all (but still has signal). If I switch the network mode to WCDMA/GSM, it gets a great HSPA+/4G signal.

I should mention that this is an AT&T model, and I'm currently using Net10 as my provider. Could that have something to do with it? Or did I damage another component on the motherboard that's used for LTE? Moreover, Net10 is an MNVO that uses AT&T towers, and we have great AT&T coverage in my area...