I posted under transmission also but need some quick ideas. I am sitting at a campground in Idaho. I stopped for lunch and when I got back in and started up the road my torque converter won't lockup. It shifts fine from 1st to 2nd to 3rd but I have to get some speed up and let up to get into 4th. When going down hill it free wheels with no tranny lockup.The transmisson doesn't slip and shifts solid. When I push the overdrive swith it seem to change but not much. I am trying to decide to drive to a transmission shop or have it towed. I can do around 55 fine. Any help appreciated

 

First thought and I dont know if it is the cause but high mount third brake light out? First thing I can think of, as well as try unplugging the EBPS or clean the tube and sensor if you have the means. Hopefully someone will post with a better understanding to help troubleshoot.

 

I have a 1999 F-350 4 x 4 Dually 6.8 V-10. I have the same problem, have change soleniod pack & torque converter, still do not have overdrive. If you find a cure, please post. Have been driving 3 months without problem other than 60 mph @ 3000 rpm, fuel mileage no so good

 

A common failure that will cause these symptoms is a failure of the coast clutch or overdrive clutch snap ring. When either of those snap rings fail that clutch can't apply.

You changed a torque converter to try to fix a no overdrive problem? I'd love to understand the reasoning behind that.

 

Sounds like a snap ring is a whole lot cheaper than what i have already replaced. If a snap ring does repair, I will still have made all repairs for less than what a reman unit would cost. I guess this is a partial payment in my continuing education.

Thank you for your help!

 

It turned out to be the snap ring and a transmission rebuild

 

Its always the small stuff.

That costs thousands.....