Model is assymetrical after rigging

I uploaded a symmetrical model in the A-pose. After the rigging was complete, when I selected the T-pose, there were assymetrical distortions to the neck, shoulder, and back. I have not had this issue before with other humanoid models. I am not sure how I can fix this without sculpting. I have a provided a screenshot of the model in Blender with the problem areas circled. Any help is appreciated.