Getting ready to drive my 2007 Classic LBZ extended cab to Florida from Mass. I will be carrying our truck camper (2700#). Wondering if using the tow/haul would help or hurt mileage running highway all the way.

I use it all the time towing my boat around town for shifting and braking.

I would suggest to use T/H all the time you run more than truck alone.
That's with a trailer, or a camper.

Above about 60 MPH the gear you run in is likely the same with or without T/H after you lighten up on the power and cruise. Only when running up through the gears will the shift points be higher, but not for a long time. And in 2nd through 6th the converter will be locked, saving a lot of heat generation in the trany. In fact converter locked will give better mileage. Accelerating without T/H, and/or with high throttle settings can cause the converter to unlock, not good IMHO.

I'd suggest that that T/H does not hurt fuel mileage, and will add much to the life of the trany.

And it appears you understand T/H and de-acceleration. Good stuff.

I'd recommend using T/H.

^X2. Recently I read a post where the person claimed better mileage with out while towing his TT. Well I just returned from a 1200 mile tow and did the first 100 miles without as a test. #9000 pound load and the mileage was 1 - 1.5 LESS without tow/haul.

Well, why not run a little test and run it all the way down one way, and all the way back the other?

There are pro's and con's, as with anything in life. The T/H mode will lock up the t/c sooner; that promotes direct power transfer, thereby saving fuel. On the downside, T/H mode also makes the engine rev a bit higher in each gear before shifting, thereby consuming more fuel.

Going down the highway for long trips, with a moderate load, I doubt it will make much difference, because if you can get into 6th gear, and the t/c is locked up (it will lock in both modes) then there really shouldn't be much difference.

One thing I caution people to consider is that the Allison is always "learning" your driving pattern. If you use T/H mode even when empty, it's developing a shift strategy for that light load, and when you put a heavy load on, it has to relearn. When I'm empty, I leave T/H off. When I'm loaded, I leave T/H on. That cuts down on the learning in each mode and gives more consistent performance.

I've found when pulling our fifth (14 to 15K) that once you get rolling on the highway if you turn off the T/H the trans will nearly always take 6th gear while if you leave it in T/H it won't take 6th until you encounter a near no load situation, as in down hill. Also in T/H the trans seems to want to downshift to 5th far quicker than when running with it off. I have not seen any difference in transmission temps running either way. Maybe not everyone's experiance but I have always gotten better mileage in in 6th when running at highway speed.

I've found when pulling our fifth (14 to 15K) that once you get rolling on the highway if you turn off the T/H the trans will nearly always take 6th gear while if you leave it in T/H it won't take 6th until you encounter a near no load situation, as in down hill. Also in T/H the trans seems to want to downshift to 5th far quicker than when running with it off. I have not seen any difference in transmission temps running either way. Maybe not everyone's experiance but I have always gotten better mileage in in 6th when running at highway speed.
X1000000, i experienced the same exact thing. no temp difference for me either.

[QUOTE=turnpike;4221495]I would suggest to use T/H all the time you run more than truck alone.
That's with a trailer, or a camper.

QUOTE]

Same here...that's how the truck is built to be used and driven.

I tow a 13,000 lb. fifth wheel trailer. I always tow at 55 mph and the transmission always shifts into 6th gear at about 53 mph. I've never driven in tow/haul mode when on fairly flat terrain. On my last trip through mostly flatlands, I decided to use tow/haul exclusively. Here are my observations using tow/haul:

The transmission never went above 5th gear, never
The transmission downshifted much sooner on gradual accelerations
The transmission temps were about the same as usual
My mileage dropped 1 1/2 mpg

I don't remember the exact wording, but the GM manual addresses the issue of when to use tow/haul mode, and it does state that it is not always beneficial unless your load is enough.

Sir you are precisely correct! Turn it off on the road or waste fuel if you choose.

With only 2700#, I would turn it on until you get up to speed, then turn it off at cruising speed.

With only 2700#, I would turn it on until you get up to speed, then turn it off at cruising speed.

With 2700# I wouldn't even bother, unless extra braking ability or downhill speed control was needed.

So are you saying to turn T/H off while towing on flat roads once up to speed? We have an annual trip to the river next month and I always dread the climb up Chiriaco Summit on the E/B I-10 outside of Palm Springs..over 12mile stretch up one of the steepest grades in SoCal with only 2 lanes in each direction. Would it be better to make the climb in manual? What are the recommended shift points/speed/correct gear/etc? I have always just left it in T/H and gone for it and left the motor/trans to do it's job. Just wondering if there is a better way to make the grade? Sometimes you get stuck behind a big-rig doing about 20mph so I'm wondering if it'd be better to be in manual so you can just tap down on the shifter to a lower gear instead of the trans feeling like it's kinda lugging to get momentum under the heavy load to get moving again. Thanks for the input!!

So are you saying to turn T/H off while towing on flat roads once up to speed? We have an annual trip to the river next month and I always dread the climb up Chiriaco Summit on the E/B I-10 outside of Palm Springs..over 12mile stretch up one of the steepest grades in SoCal with only 2 lanes in each direction. Would it be better to make the climb in manual? What are the recommended shift points/speed/correct gear/etc? I have always just left it in T/H and gone for it and left the motor/trans to do it's job. Just wondering if there is a better way to make the grade? Sometimes you get stuck behind a big-rig doing about 20mph so I'm wondering if it'd be better to be in manual so you can just tap down on the shifter to a lower gear instead of the trans feeling like it's kinda lugging to get momentum under the heavy load to get moving again. Thanks for the input!!

Yes, on relatively flat roads above 55mph turn it off so that it will generally stay in a higher gear; this includes areas where there are slight grades.
As for the hard pulls I have found that using the manual mode is far preferable. If you have an EGT guage the reason is very obvious, you will keep the tempreture down with higher rpm's which translates to lower engine load. If you leave it in drive, T/H or not, the transmission will try to hold a higher gear at a lower rpm and the EGT will rise very quickly as will all other temps to a point that when it does downshift it is harder to reduce the heat load that was already built up. When I pull the long tough grades I change to manual and raise the revs before the engine ever starts pulling down. This keeps EGT's as well as water and oil temps down and keeps power up, often even preventing the power robbing radiator fan from engaging or engaging as early as when the loading is high. You may use a little more fuel but this works best for me.

On that I-10 pull out of Palm Springs, I'd use T/H all the way up (and down) just to keep the converter locked, if and when your speed drops below 50-55. One semi passing another both about 35 MPH kinda kills your run at that hill.

For the flat land easy running, I can understand why the 6 speed guys drop T/H and let it shift to sixth. Must be nice.

I prefer to use T/H all the time when I have our trailer load on, but my load is moderate enough that I can attain and hold 6th gear even when in T/H on the highway.

Here's what we all need to agree upon: T/H is just an alternate shift strategy program; it's not a magical seperate entity that can lighten loads or flatten hills. If we all were driving manual trannys, we'd mentally be doing in our minds (and physically with our hands and feet) what the T/H program does, by trying to balance the load, engine lugging, fuel economy, etc.

Here is the simple approach to using T/H:
* If you can use "normal" mode, and not have the transmission hunt up and down gears while under load, then you're fine; you don't need to use T/H.
* If you find the tranny getting hot, and/or hunting up and down thereby shifting gears frequently, you need to use T/H to reduce the hunting and the temps.

It's just that simple.

The manual says to use the T/H when your weight is at 75% or greater than your GCWR.

I do the same. I use it to get up to speed (I tow at 60 mph) with T/H on and then set the cruise and turn T/H off. I did notice the same thing as others - with T/H on it would not shift into 6th gear. On our last trip I would check trans. temp. periodically and was only running about 115*. I do turn it back on when in lower speed situations or start getting into hilly country.

It's fine to turn T/H off at 60 to let it shift into 6th but then I turn it back on for the more agressive grade braking mode. It will stay in 6th until grade condtion requires a down shift or cruise control is disengaged and you start to slow. With cruise on and in T/H grade braking will down shift when speed hits 5 mph above cruise set point.

I tow a 13,000 lb. fifth wheel trailer. I always tow at 55 mph and the transmission always shifts into 6th gear at about 53 mph. I've never driven in tow/haul mode when on fairly flat terrain. On my last trip through mostly flatlands, I decided to use tow/haul exclusively. Here are my observations using tow/haul:

The transmission never went above 5th gear, never
The transmission downshifted much sooner on gradual accelerations
The transmission temps were about the same as usual
My mileage dropped 1 1/2 mpg

I don't remember the exact wording, but the GM manual addresses the issue of when to use tow/haul mode, and it does state that it is not always beneficial unless your load is enough.


My experience is exactly the same. However, doesn't the T/H mode increase internal pressure for better holding? I mistakenly was running boost AND was NOT in T/H on a hill and slipped the trans. The Banks system warned me before I limped, so I was able to back off in time.

Now that I have a Big Dipper trans, I doubt I'll use T/H much at all - even with the 16k GVWR 5-er.

With T/H on when towing it goes in six gear at around 61mph. and never leaves six gear till it falls under 56mph.

......doesn't the T/H mode increase internal pressure for better holding?......
When you are at highway speeds the converter is locked, believe me!

If it did happen to slip it would throw your truck into limp mode.

Tow haul would help it not to slip, but It is not like the extra pressure to your TC will increase your mileage.

When you are at highway speeds the converter is locked, believe me!

If it did happen to slip it would throw your truck into limp mode.

Tow haul would help it not to slip, but It is not like the extra pressure to your TC will increase your mileage.

Converter may be locked but what about increased pressure for the clutches?

I am not aware the T/H increases clutch pressures.

Does it?

Even if it did, I would think a slipping clutch pack would throw the truck into limp mode if it is slipping continuously.

I am not aware the T/H increases clutch pressures.

Does it?

Even if it did, I would think a slipping clutch pack would throw the truck into limp mode if it is slipping continuously.

I'll do some research about the increased clutch pressures. I agree with the slipping clutch putting the trans into limp mode.

With T/H on when towing it goes in six gear at around 61mph. and never leaves six gear till it falls under 56mph.

Depends on conditions and what you are towing; if that is what you are seeing you must be pretty light, not have much surface, or both.

I am not really sure how much my TT weights, but I don't think it's a lot. In my state we really don't have any big hills like out west. But I have towed around my state with out any problems and towed on a 60 mile stretch of nothing but hills and rollers and the truck just keeps pulling. My TT is 30ft (34ft overall) and has two slides. The wife and kid do pack it pretty full but I tow with all water tanks empty.

T/H does effect holding pressure quite significantly.... If you want to know how much and in which case it is better/worse pm Mike L he has done all the research/testing as im sure a few other builders have.

When considering Tow/Haul mode and fuel mileage, I think of the notion that a slight increase in fuel use is more ecomonical than buying a new trany.

I like to use T/H for ANY towing. Keeps converter locked:D

I am not really sure how much my TT weights, but I don't think it's a lot. In my state we really don't have any big hills like out west. But I have towed around my state with out any problems and towed on a 60 mile stretch of nothing but hills and rollers and the truck just keeps pulling. My TT is 30ft (34ft overall) and has two slides. The wife and kid do pack it pretty full but I tow with all water tanks empty.
We tow our 32 foot TT with 2 slides without tow/haul mode unless we are in the mountains and need it to help slow us down.


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When considering Tow/Haul mode and fuel mileage, I think of the notion that a slight increase in fuel use is more ecomonical than buying a new trany.

I like to use T/H for ANY towing. Keeps converter locked:D

Not so sure about the locked bit. Just returned from doing the first normal tow since break in towing and did a good bit of playing at senarios fully loaded at around 14.5K. I found on numerous occasions in T/H when I suspected an unlocked TC condition because of the odd RPM when I turned T/H off the RPM would drop about 200 RPM without a shift being involved. Tell me the converter was locked. I've done enough miles with the 1000 to know that the book ain't always right. I have never seen the DuraMax Allison get better mileage in a lower gear than what it will typically hold if you know how to control it. BTW the LML is not proving to be a very economical platform as compared to the LBZ, but the ride and other improvements make it hard to beat.

Not so sure about the locked bit. Just returned from doing the first normal tow since break in towing and did a good bit of playing at senarios fully loaded at around 14.5K. I found on numerous occasions in T/H when I suspected an unlocked TC condition because of the odd RPM when I turned T/H off the RPM would drop about 200 RPM without a shift being involved. Tell me the converter was locked. I've done enough miles with the 1000 to know that the book ain't always right. I have never seen the DuraMax Allison get better mileage in a lower gear than what it will typically hold if you know how to control it. BTW the LML is not proving to be a very economical platform as compared to the LBZ, but the ride and other improvements make it hard to beat.
Mine did the same thing, thats why I dont use t/h mode. Just watch your gauges.