2k Resolution in Full Screen

Hi all,

Can’t seem to figure out this puzzle - this happened in P3D but affecting any sim. Had some CTDs happen so I installed the latest Nvidia driver (and deleted P3D cfg). I always use full screen mode (P3D, Xplane, MSFS) and use 2k resolution in the sim (2560 x 1440) but after the update, now I get black boxes in full screen mode, which doesn’t take up the full screen. 
 

Nothing else changed - monitor the same, display port, no windows update. The only difference is a new driver. If I switch to the 2k resolution (from the native 3440x1440)  in Nvidia control panel, I get the same non-full screen view with black boxes. Going into the settings to change aspect ratio, I can override it to “full screen” but then the image is stretched and it’s not crisp/proportional to the monitor. 

I have a 1080TI with this monitor (https://www.lg.com/hk_en/monitor/lg-35wn65c-b) but can’t figure out why this changed all of sudden. Tried to roll back to previous drivers, three different ones in fact but still same issue.

appreciate it if anyone has any thoughts on this - thanks!