New Monitor 4k during boot then 1080p - Old 4k 2160p

Jun 1, 2017
GTX960 w/ Web and Cuda drivers 378.05.05.15f01 macOS 10.12 - full 4k over HDMI2 was working great!

[Old Monitor Issues]
Started having issue with older Seiki 43" 4k flickering, screen going blank and then coming back, sometimes repeatedly and often seemed to be reactive to things on the display. For example I'd be scrolling a web page and boom it would happen, go black, come back, go black, come back and if I scrolled back up it would be fine until I scrolled back down and start bugging out again. Sometimes it would happen while watching a video or reading a document or switching desktops and the temporary remedy was changing whatever just recently changed on the screen to something else. It was very much like the content being viewed was causing some sort of voltage issue. It also occurred during POST which tells me it's nothing to do with maxOS. Upon turning the PC off, the monitor would also not turn off while also having a high pitch sound from the back until I pulled the plug.

[New Monitor]
Picked up a new TCL 43S405 4k 43" confirming all the usual 4k @ 60hz both HDMI and DP supported, 15ms response time, 4:4:4 chroma...and decent reviews for a budget monitor.

[The Issues]
I initially tried HDMI to HDMI using the same cable as before. The system would boot in full 4k res (POST, Boot Loader and macOS boot process) but as soon as the login screen came up it would loose signal. If I unplugged the cord and plugged back in, you would see a quick glimpse of the login screen and then back to no signal.

I then connected to the GTX DP port w/ an HDMI adaptor and still HDMI on the monitor. The same experience during the boot screen, full 4k res, but this time the login screen came up and remained allowing me to log in, however it was only in 1080p.

The Display Prefs identify the monitor model 43S405 but gives me no options better than 1080p (even with opt + click).

When booting w/ DP to HDMI and then I swap back to HDMI to HDMI at the login screen, the display does come back on in 1080p and the Display Settings show all resolutions as expected but if I choose 3840x2160 the screen goes blank and I get "no signal" again forcing me to go back to the DP to HDMI method which again only yields 1080p even though the boot process is @ 3840x2160.

Sorry for the long winded explanation but I'm not finding any search results with anything similar to this. Any ideas what the issue could be?