BCMIF150

Not much different but mine says this in the towing section:

Activate the tow/haul feature to eliminate excessive transmission
shifting and assist in transmission cooling. For additional information,
refer to Automatic transmission operation in the Driving chapter.

And this in the driving section:

Tow/haul delays upshifts to reduce frequency of transmission shifting.
Tow/haul also provides engine braking in all forward gears when the
transmission is in the D (Drive) position; this engine braking will slow
the vehicle and assist the driver in controlling the vehicle when
descending a grade. Depending on driving conditions and load
conditions, the transmission may downshift, slow the vehicle and control
the vehicle speed when descending a hill, without the accelerator pedal
being pressed. The amount of downshift braking provided will vary based
upon the amount the brake pedal is pressed.
To deactivate the tow/haul feature and return to normal driving mode,
press the button on the end of the gearshift lever. The TOW HAUL light
will no longer be illuminated. Tow/haul will also deactivate when the
vehicle is powered down.

jgalaxy

Unless I'm on totally flat or slight downhill terrain, I lock out 6th. In general I get better hauling performance and gas mileage. Taking autoroute 15 or anything Nord is 4th and 5th territory any way. I also pull about 7900# and get similar gas mileage when I do Tremblant/Montreal (25.2l/100Km). I'm hauling to Western NY state (Pretty flat) on Sunday so I'll have better stats later on to share.

FoX2012

I towed a 6.5K load from ABQ, NM to Denver, CO with the tow/haul on it pulled up most hills in 6th easily except for steeper grades when it downshifted to 5th. The downhill decent worked like a champ...dont be surprised when it downshifts to 3rd to maintain your speed on steep downhill grades.

Towing like this netted me over 15 mpg.

IronJoce

Well you're the first one who tows 6500lbs in the mountains and get above 10mpg... Not sure how you can get that vs others

mastertinner

I tow an 8000lb tt and lock out 6th gear 95% of the time. Just got done with a 400 mile roundtrip to south west wisconsin this last weekend and went up a few short steep grades and only downshifted to 4th once the entire trip. Seems to love 5th gear when pulling this weight. I netted 9.5mpg.

IronJoce

Very similar to my mileage. And yes, 5th gear seems to work better with this weight behind, less turbo spooling.

mastertinner

Yah, I get about 10.5 at 55mph and a hair over 9mpg at 68mph.

3.7

i find that i often lock out 6th in regular suburban driving, not even towing. i've been doing it ever since i noticed that i get about one "bar" better fuel economy on my display, doing the same speed on flat ground, switching back and forth between 5th and 6th to see which is more efficient. of course for the freeway, 6th gear comes back out of the bag. it's nice to have the choice. putting that option into the truck was a win.

Buck50HD

Same here, locking out 6th gives me around 0.5 mpg better with a 26ft 7500lb tt. My mpg with this setup is 9.0-9.5 flat no wind. Much nicer towing in 5th with this much load. Rarely needs to downshift to 4th and quieter. For those getting close to 11mpg or better(lighter or open trailer), I'm guessing it would be very little difference between 5/6 and maybe better in 6th.

brulaz

That's been my experience: better mileage using tow/haul and not locking out 6th when towing ~4000# with about #1000 payload.

Tried locking out 6th over 20x on the last trip, and the instantaneous mpg always jumped (got worse) about 5-10% in 5th.