Handling noise from post processing? [GIMP]

[Morgan_Hardwood]

@okieman

As a result, I often lose smooth gradation from one tone or color to the next

Posterization.

@okieman

De-noise filters don’t always handle the specific type of noise

Denoising is not designed to deal with posterization.

@okieman

example image link (…) processed in GIMP

Only in GIMP? Use darktable or RawTherapee.
Also, you showed the end result, but that doesn’t help us understand the source of the problem. Upload the original raw file instead.