Next time this happens, try putting it in 1st gear manually with the column shifter. My truck just recently experienced the same problem as yours while towing except once I got going it still wouldn't shift. It was starting in 2nd and staying there. Only difference with mine was that it was fairly cool out at the time. Computer threw some codes and dealer ended up changing the valve body and soleniods. So far no problems but haven't towed yet. BTW, the parts where on back order so maybe this is becoming a common problem???

See my thread: https://www.dieseltruckresource.com/...ad.php?t=76325

Sticky

 

Sticky, I read your post and it sounds like my truck. I remember now that twice while in t/h it would not shift into OD, I was at 2500 rpm and had to let of the pedal and coast before it would shift and the other time I had to take it out of t/h and then it shifted into OD. Hmmm but no codes unless the ******* see codes that the key trick doesn't show??? I will also try the hand shift thing this weekend.