FF, it's hard to tell whether the OP found the solution to the problem or not. Although it may not be directly pertinent to your question to the OP, ~.tga files can be compressed using an algorhythm of "RLE compression", or they can be uncompressed. This selection is made when exporting an image file from the image processor, where there is usually an option in the dialog box when exporting, as to whether to compress the file. For trainz purposes the texture should be uncompressed. If the OP did not manage to solve the problem, and you consider attempting the solution yourself, it my be helpful to obtain the PEVsoft image2tga utility, making any changes needed, and re-exporting as a ~.tga, uncompressed.
ns