[solved] Weird texture problem (CAS project)

Hi folks! it's been years since I've did my last meshing project.

I'm creating a franken mesh project, basically is the base game leather jacket without the shirt (bare chest, so to say). Everything went fine, I have the project done. But it dawned to me I can actually do a couple of recolors of that. Basically adding a white t-shirt texture. I know, you sure are wondering why I'm adding back a t-shirt when the original had one and I took it off. truth is I hate it, and wanted to have it under the belt, not loose over it.

Right now, it looks like this:

You can see the belt on the shirt texture, but I want the shirt texture UNDER the belt, kinda like this base game outfit.

But I have no clue where to even start. Is it a mesh issue? (right now, the mesh is a clone of the nude superior part) or is a specular/normal file issue? I know I could try and shorten the texture, but I want it to fit normal pants and low pants...basically any pants I put with it.