After trying a lot of different ways, I have found that if I want to plot a rendered version of anything, I get the best results if I actually RENDER an image and the insert the image into Autocad.
I have found that this gives me the best control the final product.
It seems that when you try to plot a viewport set to RENDER, it has to render the image anyways before it plots and that seems to put a heavy load on your computer.