Is it possible someone had the coupler apart and reinstalled it wrong? I ask because I had a TON of slop, just like you are describing. I replaced the steering box because I wanted the faster ratio anyway. I installed it and still had most of the slop I had before. After talking with the vendor, I went back and started looking. Apparently the previous owner had taken the steering coupler apart and put it back together with the little shoes facing the wrong way.
I turned them 90 degrees so they were going into the coupler body the right way and TADA!! Most of my slop went away. I still have a little, but it's NOTHING like what I had. In an effort to get rid of the rest, I ordered new coupler shoes and spring. It will be here Friday and I will put them in and see if it gets even better.
