Well, youi could go to the Content creation forum, and ask if someone could teach you how to repari your own assets, giving your KUID numbers as a reference.
Looking at your AA 390, I see it has five warnings and one error. Two of the errors involve progressive meshes, which are obsolete, but might be able to be fixed with PEVsoft's PM2IM utility, available at Shane Turner's site. You're missing a "thumbnails" container, and using an aliased mesh, which although now a warning, I suspect will at some point become an error. And correcting the warnings and error in the asset and recommitting from TS12 would take care of the Trainzbuild number issue.
Members of the recently formed yesterdayztrainz group aspire to provide materials and support to permit novice content creators to enhance their skills. The group is not yet fully formed, but watch for helpful information in the future.
Another idea: look at some of the other GP38's to see if perhaps the skin you created for the AA390 could be applied to them.
I didn't check your caboose, but would expect to find similar errors and warnings.
ns