Lightroom :: 5.2 - Slideshow Image Quality / Color Rendering

I´m quite frustrated after discovering that some of my images look quite poor displayed by the slideshow module. My situation ist as follows:

LR 5.2 running on Mac OS X 10.8.5, 1:1 previews are rendered, preview quality is set to high, and I´m using a sample image showing a dark cloudy sky with some fine gradients; my slideshow preset doesn´t use any borders as I read this often causes quality issues.
 
When I´m in the Develop module, there is no problem at all, even in fullscreen display mode on my 1920x1200 display the gradients are perfectly rendered.

In Library module, when displaying fullscreen, quality is okay, but I can see some slight difference compared to the Develop module - which I understand after reading that in Develop the output is based on the actual raw data, and in all the other modules on rendered previews.

Now, when in Slideshow module, the image quality is significantly lower than in Library and I see some quite obvious banding in the gradients. I don´t have problems with blocking artifacts but the banding/posterization is considerably worse compared to a JPEG export with a quality setting of, for example, 75.
 
I can´t imagine LR´s slideshow tool would be working with a lower color depth than the 8 bit as in standard JPEGs, right? Did I miss any of LR´s parameters that influence the image quality of Lightroom slideshows or of the previews used therefore? Otherwise do you have some other explanations or hints for me in order to get this fixed? We do everything to capture our images in the best possible quality so we should also be able to present them properly after all...