JonBoy, are you lowing the BB to your lower chest (nipples), middle or upper chest?
Also, as you press the bar up, are you simultaeniously rotating the arm upwards, as if you're doing a front shoulder raise type movement? That may be why your shoulder is doing alot of the work. You could try keeping the bar in a straight line up and down and lowering it to your nipples, so the focus is the furthest away from your shoulders you can get.
Not expert advice, just trying to help.