Utah...
This may be your problem...If you are adding more tippet to an already made lader tapered to 6x, it may be that you have made a leader with too long of a tippett. Leaders (at least most of them) are made with a good length of tippett and adding more 6x to the 6x of the leader in my experience will cause the action you describe. If your butt section approached 60% of the total length you will not have that problem. If you want an extra long tippett and there are times when I use one, You may be able to correct the problem by adding BUTT SECTION as well. Try it...works for me.

Ol' Bill