So, I'm just repainting liveries. So I haven't been using the SDK for this at all. But I found my answer.
First, I had to follow this tutorial for painting the three RGB layers separately
Then I exported from GIMP using the DDS RGB10A2 format.
That was my main question, what format to save DDS in from GIMP. I don't know if that's correct, but, it worked.
I needed to lose the burnt metal look from the exhaust covers so I could paint them white. People keep thinking they are exhaust pipes, but their ejector ports, the exhaust pipes are inside the ports. I'm actually contemplating purchasing this plane if nobody beats me to it... (edit: somebody beat me to it, well, the engine needed a $70K overhaul, and, being the plane was in Cali and I'm not, I let it go :'( )
And because I keep forgetting which is which, I got this map from v_legion's tutorial (and for some reason people keep saying blue layer should be black for chrome??)
ORM (RGB) = Occlusion (Red) Roughness (Green) Metallic (Blue)
BLUE layer : no reflection (black) - full reclection (white)
GREEN layer : mirror (dark color) - no mirror (light color)