2020 Expedition Platinum w/towing package currently in for the 4th time on issue where there is binding in rear differential; initally thought it was transmission related even after having the transmission valve body replaced in February. Took in back in March, they couldn't replicate, got progressively worse over time, initally binding in the rear at low speeds when turning slightly going up hill, then at higher speeds with tighter radius (highway on/off ramp). Dealer diagnosed under TSB 24-2188, overhaulled transfer case; issue was still there when I picked up, take back for shop operations manager test drive, commits to put their best tech on it and then goes on holidays. Now back in and they have ordered parts for front differential.....don't appear to have even looked at rear differential. Symptoms can be immediatey triggered when drive selector is put in SAND mode. Mentioned HCU as possible problem from earlier posts on this thread and their eyes glaze over.