Mac Pro Late 2013 Resolution Maxed at 2560 x 1440

I can't increase the resolution past 2560 x 1440 for my Late 2013 Mac Pro, AMBD D300.

Just bought this Mac Pro off eBay with 2.7GHz 12-Core 64GB Ram thinking it can handle a Ultrawide 38" screen, but the max output resolution is 1920 x 1080.

Using with SwitchRX I wasn't about to output past the resolution. This is ridiculous! For such an expensive computer, a max resolution of 1920 x 1080?!