Gas Recirculation Valve (egr Valve) problems of the 2018 Ford Expedition

My 2018 Ford Expedition max 4x4 was diagnosed with the issue described in tcb-20-2315 in Aug 2019. The repair was done per the tcb and completed in oct 2019. The vehicle was in the shop for 10 weeks and I had to return it 4 times for additional repairs until the issue was temporarily resolved. The problem reoccured in Jul 2020 and it took over 5 visits to the dealership and intervention from Ford cust service to get the vehicle repaired in Dec 2020. I have already returned the vehicle again this time because the issue was not resolved and now will need to return the vehicle a third time. This will make 7 total attempts to get the vehicle fixed for the same issue. Ford refuses to replace the vehicle and denied my buyback request. This vehicle is a lemon plain and simple. I followed the procedures per state law in notifying Ford and allowing them to repair the vehicle. Clearly, the root cause of the issue has not been determined and the repair just completed is just a repeat of the first. This time, I was on vacation with my family in the mountains of west virginia in the dead of winter with windchills of minus 15 degrees. The check engine light and power train lights came on, the turbo shut down, and white smoke started billowing out of the tailpipe. We could barely maintain speed on inclines and had to stop for low oil pressure multiple times. We could have been stranded in the middle of nowhere with no cell reception. A problem I anticipated and expressed to Ford when I returned the vehicle for the sixth attempt. I want the vehicle replaced with the same vehicle that is not defective. That is all. Why is this such a challenge for Ford to solve? I have literally invested hundreds of hours attempting to navigate this nightmare. Attached is the letter I sent Ford in Sep 2020. The vehicle cannot be operated safely and is stuck in my driveway. I am now without a car.