Hoping someone can shed some light on my issue.
On my 2004 2500 5.9L, I tow a 10k 5th wheel camper.
Within the last year after towing with the camper about 100 miles on flat ground, the cruise control stops working and will not re-engage.
The lights are on at the dash.

Some details. When in flat ground, I do drive with O/D on. The transmission is new, less that 5k miles on it.
When I am NOT towing, the cruise works fine.

It worked fine for over 10 years towing similar weight camper.

Any thoughts outside of the text book to no drive with cruise on and not use O/D while towing?

 

I've had a similar situation while towing about the same weight. It will randomly disengage and then, whenever it feels like, it will reengage. It has never done this when driving solo. I too would be interested to know why this is happening.
John

 

Sounds like you are getting a vacuum leak in the lines. The cruise is a vacuum system.Same happened to mine (04.5) it would disengage then reset if you shut off the engine.

 

I will give that a try. Wondering if it is worth replacing the unit the vacum hose is connected to? After 11 years could it be worn out? If so can you please assist what is it called so I can order it?

 

I had my vacuum pump replaced by Strictly Diesel in Phoenix. Part number they listed was 6C3Z-2A451-A/BRPV-7 (99-07 Super Duty Vacuum Pump). The part was $241 and labor $109. Hope this helps.

 

The best bet would be to inspect the hoses and replace anything that's dried out, loose, or cracked. Don't forget anything else that runs on vacuum, like heater controls.

Then before I shelled out 400 bucks or so, I'd rig a vacuum gauge and see if low vacuum is the problem.