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I have driven trips of 30 and more miles in the dead of winter when temps were -30 and plus cold blowing snow and the transmission never did shift into OD.

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Yep, mine does it too. Normal. Even if you block the whole front-end off it will still do it: the wind flowing under your truck at highway speed is super-duper cold and it chills any heat away that the transmission is building.

Way around it? pull over to a sheltered spot, let it run in neutral for about 5 minutes or better and hit the highway again. If you have flat ground it will grab 4th and stay there. If it downshifts for a hill, you're right back in 3rd again for the rest of the trip.

Another way around it? Yes, this T.S.B. may help you.