Texture is glitching out?

If you are going to merge all parts of the mesh into one, then you need to clone something that is only made of one part, assign your mesh 0000, and import it there. Otherwise only one part will be replaced, while the rest will stay. The skin-colored patch you're seeing in the shoulder area is the remnant of the old mesh that was not replaced and it is everywhere, not only there. More about it here

As for the texture, the uvs do not connect and overlap.

You need to remove the unwanted parts of the mesh more carefully and preserve how the mesh is split into meshgroups so that it functions with other items properly:
- clone a sweater from which you want the sleeves, export the blend (call it sleeves.bend), open it;
- Delete all meshgroups that do not contain sleeves;
- select the one that contains the sleeves, disable Limit selection to visible, press B, click and drag to select one sleeves, then another, then Ctrl L - UVs;
- with whole sleeves selected, Ctrl I to invert, Delete - Faces;

- save the blend, close it;
- find the one you want to get a collar from, clone, export, delete everything but the collar, same as before, save. Repeat this process with the torso;
- find a maxis item that is of the same shape as yours, as in it has long sleeves and a high collar. Export the blend. Rename each meshgroup to r(eference)_(000)0, so the meshgroup wit cut 0000 will be named r_0, etc. Then hide them all;
- Append all meshgroups from sleeves.blend, collar.blend, torso.blend
- you need to join the meshgroup that contains most of the sleeves with the ones that contain most of the torso and the collar. Then you can remove doubles and edit uvs, if needed;
- after that you need to assign the right cut numbers to the right parts of yours mesh. Unhide r_0, find a corresponding part of your mesh, give it 0000. Delete r_0. Unhide r_1 and repeat the process until all parts of the reference are gone and all parts of your mesh have cuts;
- then you can import this blend in the package that you cloned the last (sweater with long sleeves and high collar)