I have an 06 Ram which will jump in and out of OD rapidly when letting off throttle at highway speed. This also will occur when cruise is on and a downgrade is encountered. It results in surging / bucking at around 2 cycles /second.

Ideas?

 

Push the Tow/Haul button and see if this stops it. This isnt a fix but just narrows other options down

 

Update.

My 06 3500 was surging / bucking especially when at light throttle such as just after going over an overpass on the downhill side. I thought it was going in and out of overdrive but I was wrong. It was surging / bucking but RPM's remained stable.

First, the drive line had some play in it so I replaced the 2 piece rear drive shaft with this:
http://www.doghousediesel.com/catalog/i259.html
The one piece drive shaft definitely made it smoother but it still had some surging / bucking.

Then I noticed another symptom. When in park if I revved the motor to say 2500 RPM's, it would not idle back down to the usual 700-800 RPM idle speed. It would continue to idle between 2000-2300 RPM's indefinitely until I shut down the ignition.

I was advised this was likely an injector leaking. So, never having done so before, I removed the injectors myself and sent them for testing. 5 of the 6 injectors were bad.

Interesting how the truck could run well with bad injectors. The shop said 1 was wide open leaking.

Thanks Weedahoe for the post. Interesting, pressing the tow haul button twice until "OD off" illuminated caused another related symptom. I could let off the throttle at 55 MPH on level ground and it would alternate accelerate and coast almost maintaining speed until it got below 50 MPH or so when it would just coast.