4G Disappeared topic

I flashed the Lollipop version of Liquid Smooth on my AT&T G3 and at first everything was working fine, 4G included. After a couple of days 4G disappeared. When this happened it didn't just go to 3G, it lost all data service completely. I originally figured it was the ROM and flashed back to the previous ROM I had using the TWRP backup I made beforehand. Same story, no data service. Figured maybe it was the modem so I flashed a working G3 modem on here, same story. I flashed to a different Lollipop ROM, Resurrection, to see if that fixed anything, nope. This is the ROM I currently have installed. At this point I went and look at the mobile network options and immediately noticed 1 issue, the preferred service was 3G and not LTE. I had an option to change it to LTE but when I actually select LTE it doesn't actually switch, it just stays on 3G.

The one good thing I managed to do was switch the APN to one that worked with 3G. The APN that was originally set was "pta", I can provide the actual APN information if that'll be useful but I figure most ROMs are going to have similarly named APNs. 3G works on at least 2 of the APNs listed for this ROM, "broadband" and "wap.cingular".

I called AT&T and determined that I my 4G service wasn't cut off; not that I really thought it was anyway as that wouldn't explain why I can't even select 4G as a network type. I'm kind of at a loss as to how I just randomly lost 4G access without actually making any changes to the firmware or OS of the phone. I'm also at a loss of how I can get it back.