Slideshow jerky on 4k monitor

I am using Lightroom Classic 11.2 on Windows 10 Version 10.0.19042 Build 19042.

I have an NVIDIA GeForce GTX 1660 and I am using the business drivers.

I have Quicktime 7.7.9 (it was the same before I installed Quicktime).

I have a 96 image slideshow with music an animations.

The images are jpegs exported at standard 4K resolutions (height 2160 pixels)

When I run this on my 1920 x 1200 monitor it runs smothly.

When I run this on my 4K TV (as the second monitor on my graphics card) it is very jerky.

I booted into my previous windows installation (same PC) with a version 10 Lightroom install and it runs just fine on either monitor.

I have tried standard and high quality. I have tried music on and off. I have tried blanking and un-blanking the other screen.

Not sure what to try next.

Tim

The last time I saw something like this was when I first used lightroom and I didn't have Quicktime installed.