when i make shirts and stuff i use cylindrical mapping, and before exporting the model, i define front, back, and side groups.  really helps with texturing, eliminated a lot of stretching.  also might need to define collar part and sleeve.  just chop the texture up until it maps nicely.  even if you map the entire front back side at the same time, having them defined separately helps the uvmapper make a nicer map

great looking shirt by the way