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Old 02-02-2007, 04:03 PM   #1
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GMC/Chevy Tow Haul Mode

I was just wondering if anyone has used the Tow/Haul Mode that came on my 2005 2500HD? If so, how did you employee this feature? I haven't towed with the GMC yet, so interested how it worked for others.

thanks
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Old 02-02-2007, 04:05 PM   #2
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Greeting Jim-

This was discussed once before, use the search feature, but since I'm here, whenever we are towing we always have the tow mode engaged and I keep the tranny out of Overdrive.
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Old 02-02-2007, 04:43 PM   #3
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If your towing you hit the button, it changes the shift points, it does go in overdrive.

Moreover, it down shifts to help you stop
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Old 02-02-2007, 05:00 PM   #4
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Quote:
Originally Posted by safarijim
I was just wondering if anyone has used the Tow/Haul Mode that came on my 2005 2500HD? If so, how did you employee this feature? I haven't towed with the GMC yet, so interested how it worked for others.

thanks
I find it to be excellent especially when exiting the highway or when you need to slow down...
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Old 02-02-2007, 05:01 PM   #5
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Jim,
I'm guessing that you have the Allison 5 sp. auto trans with your Duramax engine. If so, you do not have to tow in 4th gear as suggested. This trans is plenty stout to tow in 5th just as I have done with my 8.1 gas engine with same trans and rear end as you.

What I have discovered is that when and if the transmission needs to downshift, in tow/haul mode, the engine rpm is not as high as it would be if this feature was not selected. I use it this way to keep engine rpm down slightly; however, I have found that the transmission does not always shift back into 5th gear as soon as I would like it to after cresting a hill. I just take it out of tow/haul mode, the engine shifts back into 5th, rpms drop and I then press the tow/haul button again. Sounds like a pain but it works for me.

The tow/haul also give you additional braking on down hill grades but I don't use the feature with my 8.1. I just work the brakes carefully making sure not to overheat them. I believe if I was doing much up and down hill driving with the diesel, I'd get an exhaust brake (jake brake) if the size/weight of my trailer indicated it would help.
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Old 02-02-2007, 05:08 PM   #6
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The transmission that comes with the gas 6.0 liter engine also has enough muscle to tow in OD. The vehicle manual notes that it's ok. I use the tow/haul and it hangs on to the lower gears longer during acceleration, and kicks you down into a lower gear earlier if necessary. I don't see that it provides any benefit on downhill grades though. If I'm in od it stays there. To get additional braking I need to downshift to 3rd.

Bottom line read the manual and see what the manufacturer recommends. My current vehicle is the first one that ever permitted OD towing.

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Old 02-02-2007, 05:11 PM   #7
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Quote:
Originally Posted by LI Pets
If your towing you hit the button, it changes the shift points, it does go in overdrive.
the best reason i've read to keep it out of overdrive!

remind me never to follow you in a caravan....

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Old 02-02-2007, 05:17 PM   #8
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Quote:
Originally Posted by 2airishuman
the best reason i've read to keep it out of overdrive!

remind me never to follow you in a caravan....

cheer
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2air,

Give him a break, it is only a typo.

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Old 02-02-2007, 05:23 PM   #9
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I use the tow/haul mode consistently in the mountains. It does restrict the upshift to overdrive to about 58 mph. A nice feature.
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Old 02-02-2007, 06:03 PM   #10
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Tow haul is a great feature that GM and I believe Ford have offered in their light truck lines (vans too).

Tow haul basically uses the computer to manage shift points, locks the torque converter, etc. It is suggested it be used when towing and I've used it with great success. The GM version I don't believe actually turns off overdrive, but more control the transmissions ability to downshift as frequently/easily as it normally might without tow/haul on....but it will downshift if the need comes up. Transmission temps I've observed using tow/haul when towing are slightly cooler than without tow/haul on due to the constant downshifting that happens.

Bottom line, the suggestion to review the owner's manual is a great idea. Press the button (on GM trucks-- I assume Ford has them in the same place, but have no idea if Dodge has it or where it would be located) located on the the gear selector when ready and you too will be a happy camper.
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Old 02-02-2007, 06:17 PM   #11
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Quote:
Originally Posted by Silvertwinkie
...Tow haul basically uses the computer to manage shift points, locks the torque converter, etc. ...
I get the impression that from a standing start, the shift points are higher and when the vehicle goes up a grade and the transmission shifts down, I can see the tach drop further as the torque converter locks up to limit slippage with the resulting heat associated with this slippage. Would you say that is what is actually happening? Again, this is what I am seeing with the 8.1 gas and it may be different with the diesel due to programming.
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Old 02-02-2007, 07:21 PM   #12
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Quote:
Originally Posted by 2airishuman
the best reason i've read to keep it out of overdrive!

remind me never to follow you in a caravan....

cheer
2air'
What's that mean?

I have a 6 speed allison, it drops into 6 when at hwy speed??????
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Old 02-02-2007, 07:31 PM   #13
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Quote:
Originally Posted by davidz71
I get the impression that from a standing start, the shift points are higher and when the vehicle goes up a grade and the transmission shifts down, I can see the tach drop further as the torque converter locks up to limit slippage with the resulting heat associated with this slippage. Would you say that is what is actually happening? Again, this is what I am seeing with the 8.1 gas and it may be different with the diesel due to programming.
It's hard to say when the TC locks for sure in that situation. I know that on the flat road, if you tap the brakes, ever so slightly, you will see the TC unlock by the RPMs increasing. I would guess that if you see the RPMs drop, you may be seeing a TC lock situation. If you tap the brake pedal when that happens, every so slightly, basically making the brake lights come on and not acutally engage the brakes, and the RPMs go up that would pretty much say to me, yea, you just saw the TC lock and unlock.

An unlocked TC is one of the main sources of heat buildup, if not the biggest and tow/haul can help eliminate some (not lots, some) of that heat.
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Old 02-02-2007, 08:18 PM   #14
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I love my Allison 5 speed but it must be even better as a 6 speed. LI Pets, have you driven the 5 speed and the 6 speed to get a comparison?
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