Q: r9 m370x 4k / 60hz issue

Hello all -

Here's my issue:

ISSUE:

4k not displaying @ 60hz. Displays only @ 24hz (Windows 10 side only; El Capitan is fine, albeit using SwitchResX).

When runnning Windows, I'll go into Adjust Resolution and select the 4K LG TV. Then looking at the Resolution selection box, it shows the Recommended Resolution as 4096 x 2160.

Then I'll go into the GPU's List All Modes and it will show the listing for 4096 x 2160 ... BUT ... only at 24hz. In fact, scrolling thru the list, I find the highest resolution that is listed to run at 60hz is 1920 x 1080.

I've loaded all the most up to date (of what's available) BootCamp and Windows 10 software (as of June 8, 2016). But I do get a new software notification for the GPU. When I try and update, it states that "We are unable to find a driver for your system. No supported AMD hardware was detected." And so it does not install.

Like I stated above, 4K/60hz (3840 x 2160) works just fine in El Capitan ... WITH SwitchResX. Strange thing though ... there was no 4096 x 2160 listed (in SwitchResX) for the Mac.

SETUP:

2015 rMBP 15" 2.8ghz / 16gb RAM / 512gb SSD / R9 M370X GPU

El Capitan

Windows 10 Pro (via BootCamp)

4K LG TV (LG 43UH6100)

CONNECTION:

Mini DisplayPort 1.2 to HDMI 2.0a Active Adapter 4K@60H (uptab.com) plugged into the Thunderbolt 2 port.

HDMI cable 6' (purchased with the TV) between the adapter and the 4k TV (LG 43UH6100).

I'm sure I'm missing something here as the Mac side is fine; so I believe that it's not the adapter or cable but some sort of setting / driver issue on the Windows side only. Maybe somebody can offer suggestions as to what that or those "missing" things I am overlooking or not doing correctly ... it'd be greatly appreciated.

Thank you.