The things to try would be the normal thing people who can not run things. I get fill FPS no problems... but here are some tweaks to try before lowering the resolution.
1) Turn off Motion Blur
2) Lower Particle Density
3) Shadow Quality
I know you have probably done these but they make a HUGE effect on performance. Especially the 1st 2.
4) Antialiasing
5) Anisotropic Filtering
You can turn these really low without huge image quality loss.
6) Run in fullscreen mode
7) Set vsync to "adaptive"
I know you probably have done all this.. but give it a go. Again, I have everything maxed out on my Nvidia 960 so it is hard to help. I simply have no issue.. but these are the main things that will reduce framerate and should be done BEFORE changing resolution. The way to test, is of course to set 1-5 all OFF and then try it. To see if there is any improvement and then slowly add them.
One other thing people have been reporting on Steam Forum fiddling with the "afinity". I can not attest to this but I guess it is worth a try. Run MKX. Alt+TAB. CTRL+SHFT+ESC to bring up task manager. Right click on the MK10.exe and select "set afinity". Now it should show all your CPUs ticked. Untick the bottom 1 CPU, if this dose not help.. try bottom 2. While you are there you can set "Piority" from the right click menu to high.
The reasoning behind this is a console port and PS4 and Xbone both use CPU load bearing to help the GPU. So by freeing a single CPU form MKX, you have a completely free one to help the GPU.
Again, no idea if this works.. but people have been saying it dose.. so maybe give it a try. Same goes for RVB and his strange frame drops on those few stages.
Hope that helps!
Here is my douche bag answer though...
throw out AMD and buy a 9 Series Nvidia and never have comparability issues on the PC