Had the same problem, at mine it was a background process that kept using my gpu even though I ended the software.
Try this:
Pause the Texturing
Go to Task manager - Performance tab- click on the Gpu-chart and change the chart from “3D” (I think thats what it usually says) to “Compute_0”. If theres still activity even after you pause the texturing, theres a process using your resources.
Then its just to “end tasks” till you find which one it is.
-S