I am a big fan of cruse but yes, it does hurt MPG a little.
I don't care. My foot gets tired and with cruse, I can rest it on the service brake for quicker response.
If I were you, run it in manual mode on the interstate.
It will hold the gear unless it lugs to 900 RPM or you force a downshift.
The rolling hills here is plain annoying; 5th to 6th, 5th to 6th, etc.
Throw it in M and it stays in 6th.

 

I haven't really paid to much attention on my 6.7s, but, on my yukon, cruise cuts the milage by an honest 2.5 MPG. I also hit the cruise cancel when going down larger hills to avoid the downshift for engine braking, and resume at the bottom.

 

Have a safe trip. Nice rig. Hopefully the temps will warm up by the time you get to Ohio

I usually use cruise when on flats when pullin. And my foot on hills.

 

Cruise all the time.
Easy enough to use the cancel and resume on the hills.
Turning off tow haul when on the highway also minimizes downshifting and gets into 6th easier.

 

Not sure why it would be different in trucks, but cruise got me much better mileage in quite a few vehicles. I had a commute a few years back of about an hour. Did it for a few years so I had plenty of time to play with mpg and see what's what. Keeping excellent records, cruise saved me 2-3 mpg on more than one vehicle doing this route.

 

I'm glad to see others post the same thing I have to say.

Put it in manual shift mode and set the cruise! Best strategy by far. I do this with the same weight you are towing and at 65 or slightly less you should get 14-14.5 mpg depending on winds.

If you need some hill climbing power you can shift to 5, being in manual will also allow your truck to run downhill withou slowing itself down.

 

Yeah, probably does, and I would not own a vehicle without cruise. Even have it on my motorcycle.

But, we are talking towing here, and for some the cruise can make a difference.
Tow-haul mode, right foot application, engine braking (what there is) all affect the mileage.
For me I find the cruise resume from a slow speed, like coming out of a toll, is more aggressive then I would normally accelerate. So when towing I accelerate at my speed then tap the cruise.

I think that with any vehicle, you will find that people who tend to be mileage conscious will apply less right foot then what is programmed into the cruise control. Try it.

 

Did Detroit to State College Pa with my montana (about 13k when loaded) adn loved cc. There are a handful of decent grades along I-80 in Pa and never once needed to touch brake or gas. Makes the drive a lot less stressful and more relaxing for me. Set it on 65 turn radio up and enjoy. I averaged just under 12 according to dash computer on winter diesel. The truck did shift up and down often on the mountains but I could care less. If that bothers you then just lock out 6th and it should reduce the shifting.
More than anything be safe and have fun.
STM

 

I use manual mode and cruise too. Manual mode keeps the truck in 6th gear, torque converter locked up. Side benefit to this is lower trans temps.

But, if you're in manual mode, you are no longer in tow haul mode, so you don't have an exhaust brake or the downshifts as you slow to come to a light (the truck automatically downshifts even in manual mode).

I towed on some hilly terrain last weekend. I used manual mode on flats + uphills, then went back to drive and used the exhaust brake to hold my speed on the downhills.

And FYI, MPGs are more a factor of the aero of the trailer versus the weight of the cargo being towed. On these trucks, you won't feel a couple thousand pound difference in the tow nor will it affect MPG. The aero makes a way bigger difference. That's why 70MPH somehow seems to be the cutover point between decent mileage versus crappy mileage.

 

It's true you're no longer in tow haul mode when you go to the manual transmission, and the truck won't downshift to slow you down. But, you can shift down through the gears and slow yourself down just as effectively. During a slow down event from 65mph to zero if you tap the - button and keep the motor around 2500 rpm or higher it slows you down very effectively without using the brake pedal.

Whatever the engine/exhaust brake is supposed to do is irrelevant to me. Whether in tow haul or manual I still am able to use the engine and gearing to slow down or maintain a safe downhill speed. If the exhaust brake is working or not I don't really care as long as the truck is doing what I need it to.

Hope the trip is going well srkr! Kinda windy around here so I hope wherever you're at has settled down a bit.

 

My understanding of T/H is you're simply switching to another transmission programming.
When in manual mode, the truck hands over some control to you and assumes the driver will adjust as needed.
You can still downshift to a lower gear and the engine will hold the load just as it will in T/H.
In fact, M works better because sometimes I can't get the dumb thing to upshift when in T/H mode and in M I can force one gear higher to coast a bit more.

 

I like to run the hills, and ease up over the crests (unless there is a chevy in front of me, then I smoke em'...LOL)

pretty well right on 12.0 on my lie-o-meter my trips with my 9500# fifth wheel.

--
Gordon