8.75 cone sure grip locked on turns

I have a cone type sure grip in a 489 case with 4.10 gears. I had @RustyRatRod rebuild/resurface the cones and had a local shop set up the new 4.10 gears. All the parts (gears, seals, bearings, etc) I got from Dr. Diff. Also used a crush sleeve eliminator.

I put 80-90 Sae fluid in it with a bottle of AC Delco friction modifier.

However no matter what the rear end acts like it's locked when making a turn, shaking the whole rear end.

I added a second bottle of modifier, but no change.
Give it time. It'll break loose. Try doing some figure 8s slowly in a parking lot.