I have a 1999 Dodge 250o with a 8.0l v10. I was towing this weekend and everything was going fine. I tried to kick the trans down and it just stayed in overdrive. It shifts up fine. Also if I use the cruise control as soon as it is going to down shift it shuts off and the truck stays in 3rd or forth gear. And then wont shift up. If I stop the truck and shut off the key in will then shift up normally.

 

Check the tranny fluid, if it is low it can get all foamy and cause this, when you shut it down the foamy goes away and it works right for a while. It has to be able to build a certain amount of pressure to shift right and lube right.

 

Not low. It was the first thing I checked.

 

When was the last time it was changed, along with the filter.

Also, tow with O/D off, always.

 

3000 miles ago it is clean . This seems to be more of an sensor problem.