I took the tif file and converted it to PNG with no compression applied, but the color bitrate per sub-pixel were reduced to 8-bit. I keep the original resolution at 1920x1080. So right away, we have the TV scaling the resolution to 2160p and at the same time viewing a lower color bit depth. The combination of the 2 will introduce a bit more banding compare to their reference system. The tif file was about 12 Mb when downloaded. A normal conversion to PNG without going into advance settings will produce a file between 14-20 Kb. A significant difference and proof some compression is going on. Without compression my file converted to a 6 Mb file size, or half of the tif.
That being said, I did find slight banding, particulary in the reds and greens, less so in the blues. However, I was impress with the greys and whites. Still slight very narrow banding (consider the source), but it is how well the gradients were, and clipping at just the right peaks.
I also ran my DVE disc and looked at the reverse gray ramps and steps and again the gray gradients were uniform considering the disc is rec 709 and I believe 8-bit in color depth.
I did not stop there. I went to rtings website and to their picture quality page explaining gradients http://www.rtings.com/tv/tests/picture-quality/gradient
On that page they have a link to a 1920x1080 8-bit gradient test pattern. I used the Tizen web browser to open the test pattern and it gave similar results on my TV as my PNG
Test Patterns are well and good for calibrating colors and grays, but look at a 4k video with HDR and then make your judgment. After all, that is why you bought the TV in the first place.
Hope this helped.