Lightroom 7.1 SLOW (again)

I can't see a list of topics in the Adobe Forums, and a search for Lightroom Classic develop slow found nothing, so

Windows 10 Pro, Intel 5820 running 4.5 GHz, nVidia 970 GTX, 24 GB DDR4 memory, SSD for O/S, cache, LR catalog etc.  LR is the ONLY thing running that's using resources.

This is PRECISELY the same box that's been running LR just fine for the last couple years.  LR wasn't blinding fast (it never has been), but it worked OK.  At least moving the SLIDERS in the develop module were reasonably responsive, without perceptible lag.

But, with 7.0 (or 7.0.1 or whatever LR CC is since the split between the cloud and local versions), and now 7.1 installed by Creative Cloud a couple days ago, that's changed.  I'm not sure where the major performance improvements have occurs, but I'm not seeing it with either my desktop and laptop. 

For example, using the white or black sliders in the Basic module on a SMALL RAW image (we're not talking one of my D810 images, this is on a D300, 12 megapixel image).  Holding the Alt key to see the effect of moving the slider, then moving the White or Black slider causes a pretty significant lag.  For several seconds after releasing the slider, the slider moves slowly and the image changes slowly to show the effect.  This occurs WITH and WITHOUT the hardware acceleration turned on - I've tried ti both ways.  Same for using ALT with most any of the sliders.  The Black and white sliders appear the worst, but Exposure, Clarity and I suspect others also show very perceptible lags.

I've checked all the preferences and don't see anything abnormal.  This performance is detrimental to productivity so if anyone has a solution...