Display issues with Virtuacol Do-328 paint kit

Hi all,

I'm not new to FSX, or modding, having played it since the original launch, however I have come back after about 4 years of not playing and I am running into issues adding a custom livery to aircraft.

The aircraft in question is the VirtuaCol Dornier 328 regional pack version, only working on the turboprop variant for the moment until I've worked out the teething issues.

I've downloaded the paint kit, added a livery in GIMP and exported it as DDS, then converting to BMP using DXTBMP. For some reason I have got unusual shading and artifacting on the added livery, and some textures arent showing up at all, specifically interior, landing gear and the engines to some extent.

Even after swapping the affected missing textures for those being used by working liveries, they don't show up on my specific added livery.

I'm assuming this might be some sort of alpha channel issue, but I don't see how that would affect the missing textures.

Any help would be greatly appreciated, screenshots provided below for reference.

https://ibb.co/PTH6HYr

https://ibb.co/LzM7hZG