How to enable 2560x1440 option for display in Linux Mint?

I just got a new display (Samsung LC27JG50QQU, 1440p, 144hz) which is plugged into my AMD Radeon HD 6950 (DVI-D, DVI-I, HDMI 1.4, 2x Mini DisplayPort) graphics card using HDMI. However, it only lets me set 1080p max in my display settings. Cable and monitor were fine on 1440p with my MacBook Pro. I am running Linux Mint 19.1 Tessa This is the output xrandr gives:

Screen 0: minimum 320 x 200, current 1920 x 1080, maximum 16384 x 16384
DisplayPort-3 disconnected (normal left inverted right x axis y axis)
DisplayPort-4 disconnected (normal left inverted right x axis y axis)
HDMI-3 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 597mm x 336mm
   1920x1080     60.00*   50.00    59.94  
   1680x1050     59.88  
   1600x900      60.00  
   1280x1024     75.02    60.02  
   1440x900      59.90  
   1280x800      59.91  
   1152x864      75.00  
   1280x720      60.00    50.00    59.94  
   1024x768      75.03    70.07    60.00  
   832x624       74.55  
   800x600       72.19    75.00    60.32    56.25  
   720x576       50.00  
   720x480       60.00    59.94  
   640x480       75.00    72.81    66.67    60.00    59.94  
   720x400       70.08  
DVI-0 disconnected (normal left inverted right x axis y axis)
DVI-1 disconnected (normal left inverted right x axis y axis)
VGA-1-1 disconnected (normal left inverted right x axis y axis)
HDMI-1-1 disconnected (normal left inverted right x axis y axis)
DP-1-1 disconnected (normal left inverted right x axis y axis)
HDMI-1-2 disconnected (normal left inverted right x axis y axis)
HDMI-1-3 disconnected (normal left inverted right x axis y axis)
DP-1-2 disconnected (normal left inverted right x axis y axis)
DP-1-3 disconnected (normal left inverted right x axis y axis)

lspci -k | grep -EA3 'VGA|3D|Display':

00:02.0 Display controller: Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller (rev 09)
	Subsystem: Gigabyte Technology Co., Ltd 2nd Generation Core Processor Family Integrated Graphics Controller
	Kernel driver in use: i915
	Kernel modules: i915
--
01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Cayman PRO [Radeon HD 6950]
	Subsystem: Hightech Information System Ltd. Cayman PRO [Radeon HD 6950]
	Kernel driver in use: radeon
	Kernel modules: radeon

glxinfo | grep -i vendor:

server glx vendor string: SGI
client glx vendor string: Mesa Project and SGI
    Vendor: X.Org (0x1002)
OpenGL vendor string: X.Org

EDID:

00ffffffffffff004c2d560f4d325530
071d0103803c22782a1375a757529b25
105054bfef80b300810081c081809500
a9c0714f0101565e00a0a0a029503020
350055502100001a000000fd00324b1b
5919000a202020202020000000fc0043
32374a4735780a2020202020000000ff
0048544f4d3230303034340a2020014d
02031bf146901f041303122309070783
01000067030c0010008032023a801871