I have an 06 4x4 3500 mega cab. I would like to know the ins and outs of using the towing mode or OD off mode when towing a 7000 pound camper.
I towed the other day in Drive at 70 mph and got almost 13 miles to the gallon but then towed yesterday at 65 to 68 mph with the towing mode light on the dash and got 11 mpg. I thought it would have been better. I only noticed that when I slowed to stop the engine kicked in to help slow it down but it was not under powers so I thought it would not have negatively impacted the mileage.
What do others do when they tow. What is the best practice? Should I have just simply turned the OD off, that would have been worse yet.

The 5.9 seems like a dog coming up to speed but once up to 70 mph it could go all day.
Thanks John

 

Personally I only tow in 2WD for mileage purposes. I think you have way too powerful of an engine to have to put it in towing mode for a 7000 lbs camper. But I have a 5.9 v8 gasser and I get better mileage towing in 2WD so that's what I use. No OD. But it's all preference, what you're comfortable with and the weight you're towing. Because I do that exact thing, get it up to 70 and stay there, I also have a 6 inch skyjacker and 37s though so that's the best I got.

 

Tow/ haul and OD off will keep the engine running in the power band= less lugging and the ability to utilize the most available tq/hp.

As you said, shift points change and you can benefit from a little engine braking.

Keeping it out of OD will cause less downshifting and gear hunting.

Mpg and 7k lb trailer don't really go hand in hand...

That's my understanding of it anyways.

I typically lock my 6.7 out of 6th and engage Tow/Haul when towing (usually upwards of 9-10k) and don't really care too much about mpg because that's not why I bought the truck.