I am new to the diesel world and to towing. My family enjoys the great outdoors and we have finally decided to get out of the tents an buy a camper...in doing so we upgraded the SUV to a 2006 2500HD Duramax. We are buying a 29ft Travel trailer in a few weeks and had some questions about how to use the gear settibgs on the transmission. I am not too savy on this area and obviously need some guidance. How does changing the tow haul setting affect the truck and when should I really be changing the gear settings? Are there any secrets to towing that will help the life of the engine or fuel economy?

Any and all suggestions are greatly appreciated.

Tow/Haul keeps the converter locked while slowing down and commands downshifts to slow the truck using engine compression. It also holds gears longer to aid in acceleration. Manual mode is useful while dealing with long grades, a lower gear can be selected to keep EGT's low and to help in engine and oil cooling

Ok thanks...If I understand this correctly then if I am towing on a simple level grade then I do not need to worry about the manual settings, just stay in the tow/haul setting? If towing on a steep grade and using the manual setttings do you need to worry about and speed restrictions with the lower settings?

No speed restrictions, just one downshift or whatevers needed to keep from lugging the engine. On level ground I just put it in tow haul and let the Allison do its thing, no need to full with manual mode

Hi all , First post on here lots of lurking though , I pull a 32 ft that is about 10,500 give or take a bit, and on flat ground I dont even use tow haul ... you will love that truck for towing , I moved from a gasser to this and its night and day ...

Hi all , First post on here lots of lurking though , I pull a 32 ft that is about 10,500 give or take a bit, and on flat ground I dont even use tow haul ... you will love that truck for towing , I moved from a gasser to this and its night and day ...


The nice thing about tow haul is it changes the shift points including under breaking. I live in Florida so obviously hills are a minimum, but when slowing down the engine and tranny do most of the work. Saves the brakes and helps slow it down. I pull about 8K and once forgort to hook the trailer wire connector, I had to make a quick stop and almost didn't notice the difference. Use tow haul when towing. If I am running around 55, I'll click it off for a second to get the ally to shift to od, but then I click it back on once it shifts. Tow haul is you friend use it.

I agree 100 % with you . I'm just in central illinois and we are super flat around here .. I guess I should have said that in my post so I wouldn't mislead ....

Ok thanks...If I understand this correctly then if I am towing on a simple level grade then I do not need to worry about the manual settings, just stay in the tow/haul setting? If towing on a steep grade and using the manual setttings do you need to worry about and speed restrictions with the lower settings?

Well, it depends. I have a 29' bumper pull trailer as well. Weighs about 6500lb. empty and I live in an area where nothing is flat. In fact it is a a very steep windy road just to get up to where our house is at. I have never needed to use manual mode. Just set it in TH mode and call it good. I could see it for really long extended hill climbs or if your trailer is significantly heavier than mine, etc.

Point is, TH mode is fantastic. :)

I tow a 30ft TT and have no problems. I use T/H and just let the truck do it's thing. It never seems to unlock in six gear, even on the hill's. I set the cruise, site back and enjoy the easy ride. The truck can keep the speed easy and seems to just keep finding more power.

joalcann, have you towed the trailer yet, and are you buying it from a dealer or private owner? I ask because I've seen a few dealers let customers hook up to their new rigs and hit the road without getting the trailer properly set up for the truck. When coupled the truck and trailer should be level. If the trailers high in the front or back it plays hell with the aerodynamics and makes the trailer unsteady and nervous. You'll need a weight distributing hitch setup with sway control and a good trailer brake controller. All and all you'll be happy with the dmax's performance. They are excellent at towing while keeping you comfortable and safe

Ok thanks...If I understand this correctly then if I am towing on a simple level grade then I do not need to worry about the manual settings, just stay in the tow/haul setting? If towing on a steep grade and using the manual setttings do you need to worry about and speed restrictions with the lower settings?

Most of the time, you can just leave it in D and let the Allison do its thing. I really only use the manual electronic shift mode to anticipate grades - not lug the engine on the ascents and control speed on the descents). Congrats on the purchase, you'll be pleased at the power and control of the Duramax/Allison drive train.

I tow a 30ft TT and have no problems. I use T/H and just let the truck do it's thing. It never seems to unlock in six gear, even on the hill's. I set the cruise, site back and enjoy the easy ride. The truck can keep the speed easy and seems to just keep finding more power.

x2 on this one. With a 29 ft TT, you won't even be working the Duramax. Just put it in D, hit the t/h button, and drive on down the road. Don't be afraid to use cruise control, either. Interstate grades are no problem -- I've been down most of the big Interstate grades in the West (Siskyou, Parleys Canyon, Cabbage Hill, Donner Pass and others) with my TT in tow, and haven't needed to touch the brakes. I only find myself needing to manually shift on twisty steep mountain 2 lane roads, ie, when I can see a tight turn turn coming up or when I'm trying to go really slow and bumping down into 1st gear from time to time.

You'll love towing w/ the Duramax. There are plenty of hills out here in Utah and all over the west. There are literally only 3 hills on I80 between Cheyanne and Reno that make my Dmax downshift to 5th gear with my TT in tow, and even then, only for a just a few seconds on the steepest portions.

Also, it is my opinion that with a stock truck and moderate load (like you will have), there isn't much to worry about lugging the engine or forcing downshifts to avoid too high EGTs. I've yet to hear of anyone reaching unsafe EGTs in a stock truck with a moderate load. I don't worry about it in mine -- I just let the Allison do its thing.

If you can't tell, I love my LBZ!

Good luck!

Moved to Allison OEM forum.

Thank you all for the help in understanding my truck. I have not yet towed anything with the truck. We are buying the camper from a dealer and are scheduled to pick it up in a few weeks. The trailer has a dry weight of 8,500 lbs...part of the package I bought with the trailer is a sway control weight distributing hitch and they are going to also install a break controller in the truck since it did not have one.

As much as we like playing out doors the most I have ever towed is my little 14ft duck boat so this is going to be all new to me...According to my owners manual the mirrors on the truck are suppose to tellescope out for better viewing around the trailer...I can't get them to budge, is there a release button or did I miss an electic control somewhere?

Thank you all for the help in understanding my truck. I have not yet towed anything with the truck. We are buying the camper from a dealer and are scheduled to pick it up in a few weeks. The trailer has a dry weight of 8,500 lbs...part of the package I bought with the trailer is a sway control weight distributing hitch and they are going to also install a break controller in the truck since it did not have one.

As much as we like playing out doors the most I have ever towed is my little 14ft duck boat so this is going to be all new to me...According to my owners manual the mirrors on the truck are suppose to tellescope out for better viewing around the trailer...I can't get them to budge, is there a release button or did I miss an electic control somewhere?

Wonder if someone replaced them

I don't think so...they look like the ones pictured in the manual and have two sets of mirrors on each side...they look like they are designed for towing. They have two arms running from the mirror to the door I just cant get them to budge...

Give a good sharp tug straight out, they get stuck if they haven't been used. They are manual telescoping

I'll try that in the morning and see if it helps. Thanks.

Might have to wiggle them a bit. My drivers side is really tight and I use them quite a bit. Let us know how you make out

Thread kinda drifted away from being transmission related so on second consideration I've moved it to the towing forum now instead of the Allison forum.

Sorry about the bouncing guys.

Thanks guys....wiggling them worked...I don't think they have ever been extended...there was quite a bit of dirt built up inside the bars. Thanks for the help...I guess now I am just waiting on getting the camper in a couple of weeks and then take it out :-)

Is there anything I need to know about the sway control/weight distributing hitch that might be important or not covered by the dealer?

Is there anything I need to know about the sway control/weight distributing hitch that might be important or not covered by the dealer?


Rule #1 - Don't assume the dealer will help you set it up, much less set it up right.

There is an exhaustive thread on proper setup of a weight distrubution hitch over at RV.net - you can find the thread here (http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/17730894.cfm). It's a bit long, but it's 10000% worth reading and there's a 50/50 chance you'll know more than the dealer when you pickup the trailer.

I know I sound all down on the dealers, but especially during the peak RV sales seasons a lot of them hire people who aren't always the most knowledgeable. The guy who did the PDI walkaround with me on my fifth wheel when I took delivery knew less about it than I did and there was NO offer to even help hookup, much less adjust the pinbox/hitch, etc.

There are very good and knowledgeable salespeople and employees at RV dealers who know what they're doing and will be happy to help you make sure you're setup safe and properly before you pull away, but there are also the "Ok, here's your keys, good luck, See ya" type as well.

Completely agreed with privatepilot, its amazing that some dealerships release rigs to new owners the way they do. Know how to set your hitch up before hand and you'll be ok. Don't worry, they are not difficult at all. And when you get the trailer, go to an empty parking lot or another area where there is a lot of open space, set up a "site" with cones or something else soft that will not cause damage and practice backing in. I've see many people every year that get out to the campground and figure out they have no idea how to get the trailer into the site.

what part of mi are you from? what dealer did you buy from? I know a few people that use those two way radios (cheap one's $35) the driver has one and the pass. has one and will help guide you in and make sure you don't hit anything. The fun part about camping is when your walking around if you see some nice looking people that have been camping for awhile stop and talk to them and bring up some of your concerns if you have any and you should get a some good advice.

What camper where you looking at?

Thanks guys....wiggling them worked...I don't think they have ever been extended...there was quite a bit of dirt built up inside the bars. Thanks for the help...I guess now I am just waiting on getting the camper in a couple of weeks and then take it out :-)

Is there anything I need to know about the sway control/weight distributing hitch that might be important or not covered by the dealer?

These two threads will give you a sound education in a WD hitch and set-up. They are a long read but totally worth the effort if eliminating "sway" and evil handling is your goal :thumb:

Travel Trailer Hitch Set-up Procedure
http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/17730894.cfm

Weight Distribution (WD) Hitch --- How it Works
http://http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/14265335.cfm