Many things may be the root cause of "stiffness" in the shoulders or upper torso; trying to "balance" by holding your weight off the floor, insufficient use of legs and grounding, trying to "hold" the upper body to create "stillness", trying to keep the shoulders facing forward through the wrong usage of the muscles, trying to connect the body with the wrong sets of muscles, etc.
In my experience, once I found the correct way to connect my body (legs, core, back, shoulder blades, and spine) and how the opposition in the body actually works and feels, the shoulders relaxed and the body produced the correct action. One hint I might also add is that the when you use the correct opposition in the body with the back, hips, core etc. it helps one to move in a connected fashion during the weight transfer; it allows flexible movement around the spine while helping with the transfer across the foot/leg.
In my experience, once I found the correct way to connect my body (legs, core, back, shoulder blades, and spine) and how the opposition in the body actually works and feels, the shoulders relaxed and the body produced the correct action. One hint I might also add is that the when you use the correct opposition in the body with the back, hips, core etc. it helps one to move in a connected fashion during the weight transfer; it allows flexible movement around the spine while helping with the transfer across the foot/leg.