There are issues with GPU. The first thing I would suggest you try is up to the performance tab in your Lightroom preferences and uncheck the box and see if that makes a difference. It has cleared up problems for a lot of other users. GPU acceleration appears to be a work in progress at this point.
Indeed, although Live Preview Rendering still occurs, it "feels better" without the GPU Acceleration. There is less of a jump in colors, and it feels like the preview is (slightly) faster.
Wow... I am baffled by this turn of events. I mean, the GPU Acceleration has been so much hyped and talked about at the release day by Scott Kelby... The way he was talking , this GPU Acceleration was day and night with regular CPU. How can there be such a discrepancy between that information and the actual product performance?
EDIT: I just noticed this thread: GPU notes for Lightroom CC (2015)
It seems to answer some of my questions.
Thank you again for answer my post.
Apparently the biggest performance boost is seen with Mac computers with high resolution retina displays. If you look through the forum you will see an extensive thread about GPU notes. It was started by Eric Chan. I haven't followed it because I don't have GPU in my computer and I'm not concerned about it at this point.