Before I answer your question, I did see that you are connecting to a Slingbox SOLO.
This Slingbox is only a Standard Definition box. The box does have component inputs on it, meaning you can push High Definition through the box as pass-through to your TV, but you can only receive Standard Definition when viewing.
That being said, you are wondering with the performance boggles down when you select High Quality compared to Auto.
When you select the High Quality option on the SlingPlayer, the SlingPlayer struggles to give you what you want to see (a higher quality video than what the Slingbox can send you), so being that the Slingbox can only send you Standard Definition video content, the result is what you are currently see on the SlingPlayer.
When you select Auto, the SlingPlayer automatically adjusts itself to your network speeds and gives you the best video possible for the video stream being picked up by the SlingPlayer.
If you want a better video that you can watch on High Quality, then I recommend upgrading to a High Definition Slingbox that can give you the video that you are looking for.
Hope this Helps!!!
Sling Media Moderation Team