I have an 18 Platinum w/ 12k miles. Took it in at 3k due to 3rd gear shifting hard and clunking when accelerating while in 3rd. First time in, splines on output shaft were greased and sound went away for 6 months.
Took it back in as noise returned and they replaced valve body, I went in to drive it and problem was still there. They contacted Ford and they told them to rebuild the transmission or at least all of 3rd gear. They did that, I drove it and problem still there. Also cleared all codes and reprogramed. Still there.
Ford said to replace transmission, waited for that to come in and after 48 days w/out my vehicle, went in and drove it and as soon as I put it in gear I hear a loud clunk! Drove it and problem still there plus my loud clunk now. Service mgr put it on the lift and again, trans came with dry splines so they were lubed, clunk wet away but even w/ a new transmission, 3rd gear issue still there.
The 2020 rental Expedition they gave me had no such issue, service manager said now that he felt it, he drove a few he had there and all the 18's did it, the 20's did not. I am going to try to get an extended warranty from For, love the vehicle but this trans worries me and problem is still there. Will keep updating as I try to work thru this issue.