Please disconnect the USB devices and check for the issue.
If you still face any issue, please try creating a new catalog and then check.
It's not the USB devices, and it's not going to be solved by a new catalog. Use of a lot of adjustment brushes (and/or a lot of spot healing) on a photo will cause the develop module to slow to a crawl. Your symptoms are exactly what you would expect from using a lot of adjustment brushes (and/or a lot of spot healing).
Some things you can try:
- Do the brushing (and spot healing) as the next to last step, with lens corrections turned off; and as the last step, turn on the lens corrections (and all the while, please be 100% sure you have turned off the GPU ... I know you said you did, but I would double-check and triple-check)
- Do the brushing (and spot healing) in Photoshop or Photoshop Elements
- Get a faster CPU
Thank you, dj_paige! That makes sense -- when I move on to another image
and start over, LR is back to it's normal speed, but as I make more
adjustments, it eventually slows down considerably. I don't normally do
this much retouching, so I had no idea Moving on to Photoshop for
these. Thanks again!