Lots of good advice here but tough to diagnose the problem on the forum. Your sling issue could be due to it being rigged incorrectly, not having a solid position (i.e. support elbow shifting) or may be a problem with the sling itself. I have seen some nylon slings that slip at the camming buckle (the buckle with the little tab to lock it in place) when properly tensioned. Getting some in-person help would be your best bet. I am a little far away, in Riverside, but let me know if you want a hand in the IE. +1 on a weekend at Appleseed would sort out the problem.
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