I've noticed when the truck is cold it'll occasionally shift down into 4th when I put it in Drive. It won't let me shift gears manually. I thought this was something normal just because it's cold (around -20c/-4f), since it would shift into Drive on it's own after a couple blocks when it warmed up.

Last night though the transmission was at 19c/66f when I started it, and it again put itself in 4th. I couldn't switch it out and it wasn't changing over on its own. I ended up having to pull over and turn the truck off and on again, then it came on in Drive and has been fine since.

I'm taking it in on the 1st for other issues and I'm going to mention this as well but is the 'shifting down when cold' actually a thing? Or just a symptom of the same problem?

 

There is a looong description of operation the dealer can print you from the service manual, but I believe what you're talking about is just as dependent fluid line pressure data as much as temperature.


Let us know what they find or tell you.