I think this is looking GREAT! Thats a very professional and accurate looking texture/transmap combo. I think many people would stick a fork in it at this point! If you are being this meticulous about details im sure you are going to create an awesome final product and it speaks VERY well about any other content you work on in the future :)

for the shoulder strap, a few half-assed suggestions that come to mind:

1- if the tunic has properly aligned polygons, you could in Grouping Tool select a band or strap of polygons in the needed area, create a new group/mat zone out of them, or possibly export as a strap prop.

2- if the tunic polygons arent aligned in a way to make the first suggestion possible, you could possibly use the grouping tool on an existing curved strap like a lasso or reign prop from a poser tack set, then texture map or mat color the piece and parent it in place over the tunic

These are both "jackleg" suggestions, neither of which will achieve the result of a modelled garment piece of course, but may work for a quick and dirty temp solution while you are looking for modelling assistance.