I will confess that there is probably something I'm not understanding and maybe one of you can point me in the right direction or give me some good ideas.
 
Current Rig:
Core i5 4690 (Haswell)
MSI Z97-G55 SLI
16G Ram
750G SSD (OS and Apps)
1T Traditional HDD for media (SATA 6G)
Win 10 (64 bit)
Latest version of Premiere Pro
 
I'm using this for light editing. Playback with 4k files was enough to get the job done - (30fps on a single monitor at 1/4 resolution - don't need anything more). Smooth playback with cuts and dissolves, struggles a bit with fancier transitions, but if I pre-render I would get smooth playback.
 
Added EVGA GTX 1060 (6G)
Suddenly, can't play back 4k files in Premiere - SEVERE lag... skips tons of frames... forget anything nice. It even struggles a bit when playing 4k files using Windows default player.
I killed everything running in the background. No help there.
 
3D Games look great tho. 
 
So, thoughts about what I'm doing wrong? If I can't debug this, I am able to return the card but I would like to give it an honest shot first.
 
Thanks in advance.

I don't know if this thread is similar to your issue, but if so, you may find it useful > https://forums.evga.com/Titan-X-Not-Powerful-Enough-for-Premiere-CC2018-m2841444.aspx
 

Maybe the video editor needs to be reinstalled/setup to detect new card.
 
Also any hardware acceleration settings in the video editing app?
 
Is it no longer smooth if you use the reduced playback settings you mentioned before " Playback with 4k files was enough to get the job done - (30fps on a single monitor at 1/4 resolution - don't need anything more). " ?  I ask this because if you're trying to do full 4k there might be a new bottleneck.
 
 

Here's more debugging info... first, 2 screenshots... one showing the performance monitor with the Intel Graphics, the second with the card installed


Adobe forums/information seem to indicate that most video playback will be handled by the CPU. The card handles the effects it gets handed off. It would seem to be reflected in the screenshots - CPU nearly pinned with the card installed.
Now, I know the card works because I loaded up Forenite. The game looks great and plays really well.
I did not touch NVidia settings - performance setting on the card set to "balanced"
Any thoughts?

Bios update, chipset driver update, set windows power mode to performance, 
 
I don't do video editing but...
16 gigs ram might be a bit low?  Maybe faster/lower latency ram?
Are you editing on the SSD or the 1 tb platter?
Are there different codecs/4k formats you can switch to that might work better?
Is Adobe setup to use all the CPU cores?
Have you increased the memory allowed in Adobe settings?  I find it surprising you're only taking up 7 gigs RAM in your screenshot.  (my photoshop has this option)

What happens if you try editing/playback on the SSD?  You aren't getting SATA6G speeds off of a platter.
 
Playback codecs may need to be reinstalled/refreshed in windows with new video card and video card drivers.
 
"Playback with 4k files was enough to get the job done - (30fps on a single monitor at 1/4 resolution"
Is playback still happening the same?  Even though you can only see 1/4 res, maybe it's now playing back at a higher rate due to the detection of new card.
 
Although I really doubt it, I'm starting to wonder about limited PCIE lanes thru the DMI.