I have a LMM CC truck (4wd) that I use to haul a 22' toy hauler. About 9,500 lbs. loaded. I am getting 9.75 mpg, does that sound correct? Seems like I should be getting more.

My old Ford F-150 with a 5.4, lifted with 35's got 8 mpg towing. Am I doing something wrong here?

I am towing mostly flat ground with a 1 or 2 hills. For those of you in southern CA, I am getting this mileage towing to Glamis.

Picture
http://www.dieselplace.com/forum/garageimage.php?do=full&p=85428&d=1235265136

With the DPF still on the truck, that is what you can expect. I got tired of it and dropped the DPF. No warranty issues as of yet and I have been in to the dealer twice. The service dept likes the truck(s) without them also.

I am up to 12.5-13 now pulling my 9000lb boat/trailer combo at 65-70.

I get just a little less towing my camper becasue of drag, though it does seem a little low for your setup

My 2004 gets 11 - 13 mpg towing a 24' enclosed car hauler.

(That is hand calc'd my DIC is way off) . . . that just sounds funny. . . :lol:

Sounds real low to me-

I got 8.5 hauling from LA to Utah and back last month. That was with the a/c on the whole time and running 70+ through Nevada and Utah. The trailer is 20k+ and 48 feet long.

If you are getting 12-13, I have to consider the difference in wind resistance. I am towing a wall behind me. :D But nonetheless, it should be better.

Those numbers were with the DPF on, I have now gotten rid of it, so I am anxious to see the mileage increase next week. It isn't the same trip though, but should give me an idea of the improvement. Hopefully I am closer to 11.

I am getting 13-14 pulling my 8k RV, 28' long and well over 10' tall
This included Sunol grade, Altamont pass, and the grade into Holiday Harbor at Lake Shasta.
Guess I got a good one :)
Completely stock.

I pull a 33' fiver and get about 9mpg loaded, maybe closer to 10 when the trailer is empty. I thought the same thing when I got my LBZ, man this mileage is gonna be great. On second thought, mileage is a LITTLE better than gas, but I can leave all the gas trucks behind me when pulling. There just isn't any comparison when towing heavy. Your mileage sounds right on.

I get 10 to 11 pulling a 14k 5th wheel at 62/63 mph. Much faster and mileage goes down in a hurry. 62/63 gets the Allison into 6th gear.

Your mileage sounds a bit low...how many miles on the truck and how fast are you running?

I get 10-11 pulling my 30' fiver 12K or so. Doesn't seem to matter if its flat or hilly. Heard the new ones with more smog crap get a little less so your probably pretty close.

Pulling an 8-10k (depending if wet) travel trailer 55-70mph I've averaged 13.2mpg in 1,000miles. You should be getting more than 9.

For sure that is low- My toy hauler is 13 feet tall and more than twice as heavy- if I can get 8.5 then you should be doing better than 9.75.

Unless you are racing people on your way to and from Glamis:)

I agree, even if it doesn't get much better MPG, I am passing every gasser out there. :D

I get 10 to 11 pulling a 14k 5th wheel at 62/63 mph. Much faster and mileage goes down in a hurry. 62/63 gets the Allison into 6th gear.

Your mileage sounds a bit low...how many miles on the truck and how fast are you running?

I am going about between 60 - 70 most of the trip. The truck doesn't want to go slower. haha

I would say the last 1.5 hours of the trip is at about 70. So maybe my speed is killing it. I know when not towing, I start seeing a drop in mileage after 70, but I guess that might be different when towing.

Unless you are racing people on your way to and from Glamis:)

haha.....but sometimes I am down on the throttle, especially up the grades coming back on the 8.

This trip next weekend is going to Pismo, so there is just that one grade I have to go up.

I get about 9 mpg pullin my 40' wind sock. You should get better on the way too Glamis, its all down hill and with the wind. The trip home is a whole different story though.

10-12 mpg pulling 15,500# 40ft 5'er. Fuel is B-100. That's gittin' it too.

It has to be my speed then......?????

I just read also, it is better to keep the RPM's around 2000-2500.
What do you guys towing at regarding speed and RPM's?

NOTE: I have about 15K miles on my truck now.

I tow at ~62mph unless passing another vehicle...
tow haul mode in 5th or 6th depending on terrain...
my truck has ~3,000 miles on it.

With a little over 20k miles on the truck I get about 9.8 pulling the 35' 10k lb. 5er between 60 & 70 mph, that's with an elevation change from 1600' to 3500' then to sea level and then around 8.2 - 8.5 on the return trip home back up the mountains.
I get 11.5 - 12.5 pulling the 12' enclosed trailer weighing less than 3k at the same speed with less than 200' elevation change but I can get 13 - 13.5 if I keep it at or below 55 on the same road.
I think the airflow makes the difference. The 5er, being close to the cab keeps the air flowing up and over for less resistance but there's 11 feet between the cab and the enclosed trailer & the air drops down so the full force hits the front of the trailer creating more drag so the faster you go the more air resistance it creates.

with a bumper pull, you may want to look into a fiberglass shell for the bed, will help the aerodynamics alot. In CA the towing speed it 55, FWIW. The worse the aerodynamics, the more speed hurts, if you want better mpg's, slow down. Winning isn't everything, you are just racing to the next fuel stop.

I have found that my truck has a sweet spot for mileage at 65mph. The speed limit here in AZ is 75 whether towing or not. I have tried 75 and got about 8mpg. I would rather get there 10 minutes slower and run 65. Plus, if you blow a tire at 75(which I have), it's a lot easier to get that mess slowed down from 65. The towing speed in ca is 55, but I don't think anybody follows that. Even the big trucks are going almost 70 out in the middle of the desert. I go to flagstaff from phoenix pretty often, it's all uphill and i'm always pulling the fiver. Even loaded heavy, and pushing it pretty hard, I still see over 9 mpg. I think your mileage would increase if you slow it down to 65 and set the cruise control. Also, hand calculate your mileage every time so you have an accurate reading. Hope this helps.

Thanks for the input guys. I will make sure to keep it under 65 and see what happens.

Just went to Bar Harbor, Me from NJ and towed just over 1000 miles. I saw 11.1-11.2mpg avg. both ways. Have a 10k 32' 5er and was staying between 65-70mph. No cruise and PPE set at level 2 (90hp). With bigger tires, bumper and lift. Truck also just turned 11k miles. All mods listed in sig. Lovin it.

Also did an all highway empty trip, about 325miles. Left the camper in NH and am headed back Monday. Same tune and cruise set at 70, I got 18.8mpg. 70mph seemed to be the sweet spot. Any more or less and I got worse mileage.

Gonna try level 1 (40hp) tune when I return and see what it does.

I just towed round trip Dallas to Ouray Colorado. drove 70 -75 mph most of the way, had some passes to go up and down. Pulling 6500lbs a jeep on a trailer with 285 tires and got 11 mpg, before this with 245 tires I got 12 mpg. I had plenty of power at altitude and temps never went up. Love that Duramax

Thanks for the input guys. I will make sure to keep it under 65 and see what happens.
Just FYI trailer tires are only speed rated to 65 mph . . . over the past two years I have disintergated five tires . . .

And my trailer is as aerodynamic as a brick . . . a big white brick . . .

If I keep it around 60 - 65 I get 11 - 12mpg if there isn't much wind with my 30' 9000# 5er. Add a few mile an hour wind and it drops dramatically. I've seen as low as 8mpg going across I90 through South Dakota bucking a head wind.

Just FYI trailer tires are only speed rated to 65 mph . . . over the past two years I have disintergated five tires . . .

And my trailer is as aerodynamic as a brick . . . a big white brick . . .

Are you sure about this? I will have to check mine when I pick up the trailer on Wednesday.

LT tires have speed ratings, it is the 1 or 2 letter code. ST tires, are special trailer tires, cheaper then LT tires, and have a speed rating of 63-65 mph.
http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=35

Speed Rating
In Germany some highways do not have speed limits and high speed driving is permitted. Speed ratings were established to match the speed capability of tires with the top speed capability of the vehicles to which they are applied. Speed ratings are established in kilometers per hour and subsequently converted to miles per hour (which explains why speed ratings appear established at "unusual" mile per hour increments). Despite the tire manufacturer's ability to manufacturer tires capable of high speeds, none of them recommend the use of their products in excess of legal speed limits. The maximum operating speed of a vehicle must be limited to the lowest speed rated tire on the vehicle.
Speed ratings are based on laboratory tests where the tire is pressed against a large diameter metal drum to reflect its appropriate load, and run at ever increasing speeds (in 6.2 mph steps in 10 minute increments) until the tire's required speed has been met.
It is important to note that speed ratings only apply to tires that have not been damaged, altered, under-inflated or overloaded. Additionally, most tire manufacturers maintain that a tire that has been cut or punctured no longer retains the tire manufacturer's original speed rating, even after being repaired because the tire manufacturer can't control the quality of the repair.
Over the years, tire speed rating symbols have been marked on tires in any of three ways shown in the following examples:
225/50SR16225/50SR16 89Sor 225/50R16 89S

Each of these was an acceptable method of identifying speed ratings.
Early tires had their speed rating symbol shown "within" the tire size, such as 225/50SR16. Tires using this type of branding were not to have been produced after 1991.
225/50SR16112 mph, 180 km/h225/50HR16130, 210 km/h225/50VR16in excess of 130 mph, 210 km/h

Beginning in 1991, the speed symbol denoting a fixed maximum speed capability of new tires must be shown only in the speed rating portion of the tire's service description, such as 225/50R16 89S. The most common tire speed rating symbols, maximum speeds and typical applications are shown below:
L75 mph120 km/hOff-Road & Light Truck TiresM81 mph130 km/hN87 mph140km/hTemporary Spare TiresP93 mph150 km/hQ99 mph160 km/hStudless & Studdable Winter TiresR106 mph170 km/hH.D. Light Truck TiresS112 mph180 km/hFamily Sedans & VansT118 mph190 km/hFamily Sedans & VansU124 mph200 km/hH130 mph210 km/hSport Sedans & CoupesV149 mph240 km/hSport Sedans, Coupes & Sports Cars

When Z-speed rated tires were first introduced, they were thought to reflect the highest tire speed rating that would ever be required, in excess of 240 km/h or 149 mph. While Z-speed rated tires are capable of speeds in excess of 149 mph, how far above 149 mph was not identified. That ultimately caused the automotive industry to add W- and Y-speed ratings to identify the tires that meet the needs of new vehicles that have extremely high top-speed capabilities.
W168 mph270 km/hExotic Sports CarsY186 mph300 km/hExotic Sports Cars

While a Z-speed rating still often appears in the tire size designation of these tires, such as 225/50ZR16 91W, the Z in the size signifies a maximum speed capability in excess of 149 mph, 240 km/h; the W in the service description indicates the tire's 168 mph, 270 km/h maximum speed.
225/50ZR16in excess of 149 mph, 240 km/h205/45ZR17 88W168 mph, 270 km/h285/35ZR19 99Y186 mph, 300 km/h

Most recently, when the Y-speed rating indicated in a service description is enclosed in parentheses, such as 285/35ZR19 (99Y), the top speed of the tire has been tested in excess of 186 mph, 300 km/h indicated by the service description as shown below:
285/35ZR19 99Y186 mph, 300 km/h285/35ZR19 (99Y)in excess of 186 mph, 300 km/h

As vehicles have increased their top speeds into Autobahn-only ranges, the tire speed ratings have evolved to better identify the tires capability, allowing drivers to match the speed of their tires with the top speed of their vehicle.

Most ST rated trailer tires are limited to 65...but not all of them. Check yours to be sure, one way or the other.

I knew all tires were speed rated, but I just never thought to check mine. Or even think that they might be limited to 65.

Maybe the 285s on your truck are messing things up a bit.What mpg pulling did you get before getting the larger tires?

I never towed with the 245's.... those were gone the first chance I could get rid of them.

After this weekend, I will post the mileage I got.

AFAIK all ST class trailer tires are speed rated to 65 MPH . . . I have never noticed it written on the actual tire, but if you look up your tires on line they will tell you.

I have detonated PLENTY of trailer tires driving 70 MPH . . Granted there most likely was an accumulation "issues" that going 70 MPH exposed . . .

I'm happy trucking along at 65 MPH now . . .

You should be getting better and likely will. I tow a 29' fifth wheel with about the same weight you are towing, except about 12' high. We took a 2000 round trip to CA and back to central WA via 97 and I-5. Pulling all those hills and such averaged 10.8 for the whole trip earlier this summer. Had the speedo set at 62 mph. I was hoping for better but am happy to be in double digits. Mine just rolled over 20k miles this week.

With an LBZ and in favorable conditions I can get 12+ towing a 10K lb 5th wheel although overall average I get high 11's.

Many reasons to drive at 65 or less. You blow a steel belted radial and don't notice it, it can tear your trailer to hell and cost you $1K or better to fix. Seen it, got the t-shirt. Friends trailer looked like it had 3 sheets of plywood blown up inside of it after he lost a tire. If your towing a decent sized trailer maybe better then 8K lbs then invest in some decent tires and not the chinese ones that usually come on them.

If you care what Math tells you then Aero HP= frontal area * speed squared* coefficient of friction. In layman's terms you can do nothing at all to our trucks to be able to beat the speed problem but drive slower. 18 wheelers driving all day everyday can derive some long term benefits from a wing but us weekend warrior monkeys can't do crap.

Do 65 and save the money for camping.

I just towed with a friend who was pulling a car in a trailer with a gasser suburban. he weighed his rig, about 14k total and 7.5K for the trailer. He was getting 10 mpg.

I tow with an open trailer so my trailer weight loaded is about 5K. I cruised at 61 while he tried to keep up and got 18 MPG.

I posted this because what you guys are posting with similar weight trailers for our trucks does not seem much better than what he got from a gasser.

Only difference was when he radioed and said he had to go down to 3rd gear to climb that hill to which i replied, what hill?

Are you sure about this? I will have to check mine when I pick up the trailer on Wednesday.
I dunno about the 65 mph rating... more likely he had some cheap tires made in China that there was a lot of posting about over in the Rv.Net Trailer Life forums. EDIT: Perhaps the ST tire issue at play as well...

I have an LB7, so not really the same but I get 10-11 towing around hilly New England with my 14K 35' 5ver. Edge on level 1 usually. I set the Cruise control at 70 and let the D/A do the rest. I find any lower and I am constantly shifting, any higher and just dumping fuel.

I just got back from the trip and got 11 mpg towing back. That is with 1 grade and some traffic. It is hard to say what it was going out because the traffic was worse going, but it ended up at 9.5 mpg. I am sure that would have been better without all the stop and go.

I will say that downshifting (4th) and keeping the RPM's at 2500 going uphill or slight incline really helped. It also dropped the EGT's about 200 degress, compared to having it in the next gear. (5th). My speed was between 60-65 most of the way. I don't think the EGT's went over 1200, and if they did, it wasn't for long.

I have the Edge Race, and the turbo brake on level 2 worked awesome.

I just got back from SC to NY towing a fifth wheel about 12,000lbs. got 9.7 to 10 no matter what speed. All stock 09 GHC Dually 4,000 miles.

In my experience, there is a substantial difference between 65 and 70 mph in fuel consumption towing. I get about 1.5-2 mpg less at 70. But that is with a 5er.

I dunno about the 65 mph rating.. . .Perhaps the ST tire issue at play as well...




Beleive me . . ST trailer tires no matter the brand, are only speed rated to 65 MPH . . . does it clearely say on the sidewall . . . no . . . but look on-line . . . I was shocked too . . .

Check out Goodyear or Maxxis . . . ST Trailer tires are rated to 65 mph. . . .

See the PDF from GY: http://www.goodyear.com/rv/pdf/marathon_gen_info_032806.pdf

See Maxxis: http://www.maxxis.com/Repository/Files/m8008load.pdf

My truck gets between 10 and 11 mpg pulling my 27' enclosed trailer. It also doesn't seem to matter if the trailer is empty (4400lbs) or loaded (10500lbs). I just pulled the trailer loaded from Santa Maria, CA to Ogden, UT (loaded) and back (empty) at 65 mph in CA and 75 mph in all other states and averaged 10.82 (loaded) vs. 10.78 (empty). I just completed the PPE air box mod with the DRC mod and removed my muffler. I am making the same trip again on monday, same route, and i will post my mileage again to see if the mods changed anything.

I pull a 28 foot travel trailer with an 04.5 LLY. Best mpg I have gotten is just under 13, running about 57 mph. It is the air resistance that starts jumping up above 55 mph that causes the drop in mileage. That is the reason why the speed limit was set at 55 back when we had the fuel crisis a bunch of years ago. It is just physics.

I am going to either buy or build an aerodynamic nose cone for my trailer so its not like dragging 2 sheets of plywood down the road. Its like having a parachute or air brake behind you. I spoke to a company that makes fiberglass nose cones for box trucks and they said they would help me size one for the trailer.

If you get on google and get the right search criteria, an forum posting/article is out there on the web. A guy detailed how he built a nose for his trailer and the mileage gains that he got by getting it to cut through the wind. For those of us with pull behinds, the wings don't do any good. They have to be close to the trailer (like 5th wheels) to get the wind going up and over the trailer.

My truck is stock except for 265's and having the 06 airbox assembly and turbo mouthpiece to cure the overheat, choked breathing condition that the trucks had.

dc

Just FYI trailer tires are only speed rated to 65 mph . . . over the past two years I have disintergated five tires . . .

And my trailer is as aerodynamic as a brick . . . a big white brick . . .
Goodyear G64 are rated @ 75 mph

Goodyear G64 are rated @ 75 mph
UIAM, they require a 100 pound capable rim. The Michelin XPS are steel tread and sidewall — rated at 80 # rim — not limited to 65 mph..

just returned from a trip from San Jose CA to Auburn CA and return...
run ~58mph both directions...
14.7 on the way up and 14.0 (Regen noted) on the return trip...and I pull a 28+' Travel trailer near 8,000 pounds. My truck now has about 5,000 total miles....and the towing mileage has remained about the same since the first week I got it. :)

I just replaced( about 1 month ago) my 9 year old original equipment Goodyear Marathons (load range C) with a new set of Maxxis Load Range Ds, in 225x75x15 size...hope they wear as good as my original Marathons.
This was my second trip on these new tires....seem to be wearing nice and evenly and no other issues noted.

I pull a 28 foot travel trailer with an 04.5 LLY. Best mpg I have gotten is just under 13, running about 57 mph. It is the air resistance that starts jumping up above 55 mph that causes the drop in mileage. That is the reason why the speed limit was set at 55 back when we had the fuel crisis a bunch of years ago. It is just physics.

I am going to either buy or build an aerodynamic nose cone for my trailer so its not like dragging 2 sheets of plywood down the road. Its like having a parachute or air brake behind you. I spoke to a company that makes fiberglass nose cones for box trucks and they said they would help me size one for the trailer.

If you get on google and get the right search criteria, an forum posting/article is out there on the web. A guy detailed how he built a nose for his trailer and the mileage gains that he got by getting it to cut through the wind. For those of us with pull behinds, the wings don't do any good. They have to be close to the trailer (like 5th wheels) to get the wind going up and over the trailer.

My truck is stock except for 265's and having the 06 airbox assembly and turbo mouthpiece to cure the overheat, choked breathing condition that the trucks had.

dc
That cone isn't going to do crap for you. Ask any RV hauler if they have one--- they don't and it is because it isn't worth it!

I get 7.9 at 65 pulling my 5ther. At 55 8.9.

Just got 12.9 (DIC) in mountains and flat at 60-70 with our 12K+ 5er. Have 10K miles on truck. Wind and speed make a very large difference.

Just pulled my 12K high profile 5ver to Yellowstone and back from Tucson. Averaged 11.5 for the trip (Hand calculated, total miles divided by total fuel). I usually set the cruise at 1900 rpm. Saw a high of 13.5 (DIC which means about 13 for me) on the flat sections of I-15 in Utah, to a low of 9.2 (again DIC, probably closer to 8.7) in the mountains.

05 C4500 with a four horse trailer (two horses in it). I got 12.5 MPG round trip to St. Louis! Not bad.

Just returned from hauling our Featherlight horse trailer (4H, weekender LQ, 2 horses aboard) round trip from Kingston, TN to Ft. Robinson, NE. Total milage was just under 3000. Got 10.1 mpg for the entire trip. Cruise was set at about 71 mph for most of the run. Trailer weight was probably 13,000 more or less.

Just returned from a trip from the Fort called Worth to the Fort called Collins in Colorado, by way of US 287 thru Texas and New Mexico and I-25 thru Colorado (this part of Colorado all formerly part of Texas - given up to the Feds upon entry into the Union in 1845 in return for the US paying off our national debt - perhaps a bad trade?).

Till this trip I manipulated the tranny into shifting to 6th at 60mph by going briefly out of tow/haul, then back in, thinking it would be better for diesel mileage, and got about 10 mpg @ 60mph going north and 11mpg going south. 18' travel trailer weighs about 4200 lbs loaded. But it has a big wind load because the frontal area is the same as longer trailers.

This trip I left it in tow/haul the whole way, and tried various speeds from 60 -70mph: At 60mph I got 13.8 - 14.5 (terrain & wind varies - 3 fills to get there) going north and 14.0 -14.8mpg southbound, all in 5th gear (never shifted up - decided to "trust" the Allison). Yes, this is actual math, not the digital readout, tho they were similar.

Pleasant surprise. Another good reason to use tow/haul when towing. Of course, the "holding speed when in cruise on the downslopes" is another good reason to use the towhaul, which was most useful when on several 12% grades coming down from Pingree Park on the backroads to Fort Collins. Temperatures on the tranny and engine (factory guages) stayed "normal" {150* tranny and 210* water}. Never heard the fan. 90* in Texas, 75* in Colorado flatlands.

What do others think about NOT getting into 6th gear and holding speed to 60mph?

What do others think about NOT getting into 6th gear and holding speed to 60mph?
Excellant Idea T.H. always when towing and never above 5th gear.
Maintain at least 1800 rpms on flat and 2200-3000 on grades.

The engine temps will be cooler which this makes for a more pleasant trip.

So you are pressing and holding the tow/haul button (for some period of time, then releasing it) in order to lockout 6th or ?

Pressing and holding it in will lock out overdrive (6th gear ) ...:chevy:
tapping the button will put you in tow / haul mode this keeps you out of overdrive also
besides extending the RPM ranges between shifts ...

Pressing and holding it in will lock out overdrive (6th gear ) ...:chevy:
tapping the button will put you in tow / haul mode this keeps you out of overdrive also
besides extending the RPM ranges between shifts ...

I am not too sure that just "tapping the button" will keep me out of overdrive, because I'm sure I've been in 6th gear when towing 65mph, 1600 rpm-ish. I'll have to try the press and hold method though. I don't tow as often as I'd like too...

I am not too sure that just "tapping the button" will keep me out of overdrive, because I'm sure I've been in 6th gear when towing 65mph, 1600 rpm-ish. I'll have to try the press and hold method though. I don't tow as often as I'd like too...

If you are at 1600 rpms @65 mph yes you are in 6th gear.
This is why you manual shift to stay out of 6th gear.
On this "tapping the button" I am not understanding what you hope to achive other than confusing the transmission.
Push the towhaul button to put it in towhaul when towing and leave it there, start to finish.
When you make a stop and shut down remember to push the T.H. button again if you are still towing.
When you are not towing leave it out of towhaul.



Q. Tow/Haul vs. Normal Mode - If I use use Tow/Haul without a trailer, , is that a problem? And vice versa?
A. T/H can be used at any time, even when not towing. Some drivers may not like the T/H shift characteristics when the vehicle is lightly loaded, and thus normal mode would be selected. When not heavily loaded, some drivers switch from Normal to T/H mode during closed throttle downshifts from highway speeds to help slow the vehicle and then switch back to Normal mode after they've stopped. If the driver chooses not to use T/H when towing or heavily loaded, he/she can expect to see higher transmission sump temperatures, more wear and tear on the brake system, and increased shift cycling.Back To Top (http://www.allisontransmission.com/service/faq/index.jsp?CategoryID=11#TOP)
Q. Tow/Haul vs. Normal Mode - What's the difference between Tow Haul and Normal Mode?
A. Tow/Haul (T/H) shift mode significantly changes the transmission's shift pattern to reduce shift cycling and to deliver better performance, control, and cooling when towing/hauling heavy loads. For instance:
Upshift points are raised at light to mid throttle position to use more of the engine's available power for accelerating.Downshift points are raised to enhance engine braking to help slow the vehicle.
During deceleration, the torque converter clutch (TCC) remains applied at closed throttle to much lower vehicle speeds to significantly improve the effect of engine braking.
During acceleration, the TCC is applied in 2nd range and remains applied in 3rd, 4th, and 5th. This improves the drivetrain efficiency and significantly lowers transmission sump temperature when towing heavy loads. In Normal mode, TCC generally applies only in higher ranges and is dependent on throttle position.Back To Top (http://www.allisontransmission.com/service/faq/index.jsp?CategoryID=11#TOP)
Q. Tow/Haul vs. Normal Mode - When should I use Tow/Haul? A. T/H mode is recommended whenever you are towing or the truck is heavily loaded, for all the reasons noted in the above question.

Somemore reading for you "admranger"

http://www.allisontransmission.com/service/faq/index.jsp?CategoryID=11#92

Pressing and holding it in will lock out overdrive (6th gear ) ...:chevy:
tapping the button will put you in tow / haul mode this keeps you out of overdrive also
besides extending the RPM ranges between shifts ...

Not on the six speeds. The button only toggles between TH on/off. Since the six speeds have tap shift they don't need OD lock out. You just use the tap shift to select any gear you like.

What Edwin was saying "I manipulated the tranny into shifting to 6th at 60mph by going briefly out of tow/haul, then back in" is if your at 60 mph in TH you are not going fast enough for the Allison to shift into sixth. If you momentarly toggle out of TH it will shift into sixth then toggle TH back on and it will stay in sixth unless speed or engine load drop it out.

Not on the six speeds. The button only toggles between TH on/off. Since the six speeds have tap shift they don't need OD lock out. You just use the tap shift to select any gear you like.

What Edwin was saying "I manipulated the tranny into shifting to 6th at 60mph by going briefly out of tow/haul, then back in" is if your at 60 mph in TH you are not going fast enough for the Allison to shift into sixth. If you momentarly toggle out of TH it will shift into sixth then toggle TH back on and it will stay in sixth unless speed or engine load drop it out.

That is EXACTLY what I used to do, thinking that the lower rpm in 6th gear at 60mph (and in tow/haul) would equate to better diesel mileage, but IT DID NOT WORK. I got significantly better (like 3-4.8 mpg) mileage in 5th gear (and in tow/haul) at 60 mph than I used to get in 6th gear (and in tow/haul). I also saw slightly lower transmission temperatures.

My 2004 gets 11 - 13 mpg towing a 24' enclosed car hauler.

(That is hand calc'd my DIC is way off) . . . that just sounds funny. . . :lol:

That look about what I get in mine...