As you can see the torso does not move with the rest of the body. I absolutely don't have any clue how to deal with this. Help, anyone?

Your mesh has no morphs. Is this an EA mesh, a mesh you made yourself, or another creator's custom mesh? Which tool(s) are you using to make it, if it's yours (meshing program, CTU/TSRW and so on)?

Oh, god. I should've put in a little more info. Anyway, this is an edit of EA's long sleeved tee and I'm using CTU and Milkshape.

*edit* It was working fine when I tested earlier versions, what... how come the morphs don't work anymore?

How did you edit the shirt? I assume you modified the mesh since you mentioned Milkshape. Did you add or remove any vertices? (This is not your immediate problem, but this will break the morphs.) What steps did you take in CTU? By default CTU keeps the links to the original morphs for the mesh you're cloning, since they usually work fine with a mesh reshaping.

You'd probably be best off by just building a new package with CTU. Make sure you have the original EA shirt selected, create your patterns, import your modified mesh, give it a new name, and Save As to make your package. After that point you can open the package with CTU, make changes to patterns, and save. If you need to change the meshes or textures IMO it's better to use S3PE to replace the file.

I tried repackaging it in CTU again but I still get the same result, so I ended up just editing a new mesh (and just packaged that instead) and it all works fine now. Thanks for the help it was very much appreciated. :D