I just got a 2022 F350 Lariat and, in reading through the specs (page 238 of the owners manual), it looks like when the vehicle is in 4H and the locking differential is engaged, the maximum speed that it will allow is 25 mph before it Auto disengages and then it will reengage at 20 mph. With the vehicle in 4L and the differential engaged, the max speed is 62 mph before it will Auto disengage and then it will reengage at 55 mph. This does not make any sense to me. I have had a 4X4 of one kind or another for many years and have never even attempted to go 55 in 4L. Honestly, not even sure that my vehicles would have if I tried. This rating seems backwards to me - IE - I would expect 4H @ 55mph and 4L @ 20mph.

What am I missing? If anyone can explain this or knows the reason for it, it would be greatly appreciated.

 

Wheel speed in mud on slick rocks can get to that speed. You wouldn't ordinarily be in your high gears while rocking.

 

But, that's the point, you won't go that fast in 4 low, especially on hard surfaces with good traction.
And, you could sure break something if you had the diff locked up at higher speeds than 25 on surfaces with good traction.
I left mine locked a few weeks ago after pulling a trailer out of the mud, forgot to turn it off, and when I turned out onto the street and the rear axle started popping, sure made me jump before I could twist the **** to off!

 

It seems nonsensical yes, throws a lot of people off, but it has to do with spinning wheel speed when stuck not ripping down the road driving. Once you think about it that way it makes sense.

 

Thanks all. That does make sense now. Appreciate the feedback.