Not super experienced with transmissions in life, so figured I'd try to post this here, and see what the feedback is. Will be calling the local dealer this week, but wanted some second opinions first:

Background info: 2019 Supercrew XLT shortbed with the 2.7, 4x4, 10 speed, and BF Goodrich KM3's, stock size and no lift kit. Factory tune and almost always drive in normal mode barring ice or occasional towing. The transmission has generally behaved (I'm approaching 50K miles), and it's been serviced regularly - every 4-6 months generally but never more than 5K miles in between. Transfer case fluid was changed at ~40K. Prior to transfer case fluid change, shifting had been behaving more rough than out of the factory, and noticeably improved temporarily afterwards.

Long story short I was on about a 2 hour drive a little while back (at about 49K miles), and not going to lie, was being a bit of an idiot and going about 90 -100 in my truck for an extended period of maybe 30 minutes or so on dry road. Wasn't (obviously) towing or carrying much weight. At some point at approximately 95MPH, the transmission suddenly began going haywire and gear hunting, as the truck started bucking like a bronco at high speed. Sensing something was wrong, I immediately took my foot off the gas and began allowing the truck to decelerate. I thought about pulling over, but did not want to brake to force the truck to downshift hard. However, as soon as truck speed dropped below 80 miles per hour, it seemed to start behaving again and the bucking stopped. At 60, I lightly tapped the accelerator to see if the truck would accelerate normally and it did. I checked transmission temp next, and it was quite high at ~221 F but not catastrophic (my understanding is most synthetic tranny fluids are fine at those temps, and the transmission only starts to get heat compromised above 235 F, with 240+ being uh oh time. So I decided to try for the next rest/service area, which was still about 20 miles away, and keep going easy on the truck until I got there while monitoring for any sense that anything was very seriously wrong - hoping/praying that I hadn't broken anything.

During this time, the truck behaved more or less normally. However, there were a few hills where the transmission downshifted for more torque. On one, I noticed white steam coming from underneath the truck (tranny temp was dropping but still above 212 F at this point so I wasn't sure what this was, but figured steam possible) and it was coming from underneath the truck NOT the exhaust. Tranny temp continued to drop with going easy. By the time I reached a service area, we were back down around 186 F and the truck was generally behaving normally, though it would occasionally buck when shifting in some of the lower gears (which was something I'd intermittently experienced before, especially prior to the transfer case fluid change at 40K). We let it cool off some more, and since I didn't feel qualified to attempt anything bold with the 10 speed like trying to change the tranny fluid myself at a rest stop 100 miles from home (and we were going somewhere we had to be), resolved to keep driving (gently) then take it in for service sometime after I got back. I've been taking it easy on the truck since (it completed that particular trip, and has only been driven locally since), and now it's time to try to fit in an appointment after the holidays.

Shifting has generally been normal since with the exception of lower gears (up and downshifting around either 3rd or 4th is sometimes rough), and I get the sense the truck bucks when shifting forward to reverse. At the rest stop, the underside of the rear differential was stained dark as if wet, but I didn't see any fluids. We stayed there for a while, and I did not see stains on the asphalt below the truck, so I'm confident nothing was actively leaking. Hours later, the rear diff was still stained, which tells me this wasn't water.

So, experts:
-Should I be concerned? Did I maybe crack something or blow something up? Is/was my tranny fluid not circulating properly?
-Yes, I'm an idiot for going that fast for that long in a truck - did I just momentarily overheat the tranny and everything's more or less OK other than maybe shortening its life? Or did I possibly really break something that's just a ticking time bomb.
-If the tranny was the issue, why the dampness on the underside of the rear diff?
-What was up with the white steam? Would a Ford dealer ever use non-synthetic tranny fluid which would overheat at 220?

Any and all expert opinions welcome - going to take it in soon and want to be informed about the possibilities before getting a diagnosis from someone who I won't get to face to face with to tell them how it happened.

Thanks and Merry Christmas!

 

Welcome to FTE,

Had a very similar thing happen to my wife’s former Navigator. Took it to the dealer and they tore the transmission down. Discovered sun gear 3 had a blown seal. They had to rebuild it because there were no transmissions available from Ford, so she was without it for 2 weeks. That was back in May or June. They didn’t keep us informed, just returned it and said they rebuilt it.

 

If it is not having issues currently, my guess they will say 'no issue'. I guess it could have thrown a code they could detect, it would be nice to have a documented concern on record with them. I would tend to leave out the mph detail, just say hwy speed. The dampness by rear end, again if it isn't dripping, it's not leaking. Good luck, mine has not had any issues like that, does some goofy low speed shifting at times.