I hope I am not violating some rule but I posted this on the 24Valve Drivetrain forum with only one response.
So will try here.
My brother bought a 98 2500 with the CTD last month, 80,000 miles on it and an automatic, (tried to talk him into a 6speed like mine but his wife likes autos).
He pulled his 35ft 5th wheel for the first time last week and had some strange goingson.
After stopping for fuel, pulled on to freeway, noticed a, as best he could describ it, feeling/ride like bad expansion joints in the road, starting around 40 mph, had the OD locked out, it continued up to 60/65 mph when he tried using OD, it smoothed out, there was no variation in engine speed, tach stayed solid durning the "bumping".
He tried locking and unlocking the OD a couple more times with same effect, kinda a bumping with OD locked out, then on 3rd or 4th try, all ok in or out of OD.
Anyone have any thoughts.
Tranny fluid is 100%., looks, smells OK.
Could not find similar prob in other posts.

 

That sounds strange. I guess if I were you I would post a message for Bill K. at www.dieseltrans.com. That way you will get an informed answer.
Tom

 

Thanks Tom.
Will Do