Basically, the two bones that stick out in your upper back (most visible in skinny guys) should be brough up in order to flex your traps. I don't know how you would do this but you have...
I have also been having trouble with my grip and this big guy introduced to me a good way to strengthen grip. Deadlifting often is obvious but he took a bar (small bar), tied a rope...
I'm on SS as well but hella weaker than you. You must have a lot of natural strength if you're able to increase weights like that although you shouldn't be doing that. Just go with the rule: 5 or 10...