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2008 Silverado 2500 6.0
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Discussion Starter · #1 ·
When I put my truck in tow/haul mode it will down shift hard on a level road at a steady speed. Starts after the tranny warms up with or without load.
 

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That's what it is supposed to do... hold lower gears longer. If you're not going fast enough for what T/H parameters call for, it will downshift to a lower gear until you increase speed.
 

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When I put my truck in tow/haul mode it will down shift hard on a level road at a steady speed. Starts after the tranny warms up with or without load.
I dunno, but we're not really supposed to use it unless you are 75% or more of your GCWR.
 
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Some drive with T/H on all the time. Doesn't hurt anything at all. All it does is hold lower gears longer. It will hurt gas mileage.
 
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2008 Silverado 2500 6.0
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Discussion Starter · #5 ·
I dunno, but we're not really supposed to use it unless you are 75% or more of your GCWR.
I dunno, but we're not really supposed to use it unless you are 75% or more of your GCWR.
I have had the truck since new 25 miles it now has 260,000 miles and this just started . If I’m going say steady 55 miles mph on a level road towing my trailer it will down shift pretty hard and not change until I let off the gas or turn off tow/ haul mode. Turn on tow/haul back on and it will do ok for a few seconds then downshift again .
 

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Still, it sounds like the trans is doing what it's supposed to do.

Anything else different? Taller tires, heavier load in the bed or trailer? Wind?
 

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2008 Silverado 2500 6.0
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Discussion Starter · #9 ·
Still, it sounds like the trans is doing what it's supposed to do.

Anything else different? Taller tires, heavier load in the bed or trailer? Wind?
This is not normal as I can’t use t/h mode as it revs way to high and won’t stop until I turn it off or let off the gas. I’m talking level road not pressing the gas hard didn’t do it for 250,000 miles this just started.
 

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1999 Silverado LT LQ4 2006 Sierra SLT LBZ
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This is not normal as I can’t use t/h mode as it revs way to high and won’t stop until I turn it off or let off the gas. I’m talking level road not pressing the gas hard didn’t do it for 250,000 miles this just started.
That is literally what t/h mode is supposed to do lol
 

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2008 Silverado 2500 6.0
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Discussion Starter · #12 ·
That is literally what t/h mode is supposed to do lol
How can you say that . It is UNUSABLE unless I want red line the engine going 55 miles an hour or less.
That is literally what t/h mode is supposed to do lol
the t/h is supposed to downshift for braking or to keep speed up when hauling or just driving without trailer . Not rev up 3000 rpm for mo reason. I have driven this truck for 250,000 miles and have put 1,000,000 miles on my other GM trucks with t/h and never had that issue.
 

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1999 Silverado LT LQ4 2006 Sierra SLT LBZ
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Does it shift when it gets to red line?
When you turn t/h mode on it is normal for RPMs to jump up a bit because you are no longer in over drive I believe. Something alone those lines
 

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2013 Sierra SLE CC 2500HD Duramax
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I have never experienced what GM Jeff has on his truck. With my 1500 6 speed while in T/H mode it would take longer to upshift. I know it revved higher but at what I have never noticed exactly. It wasn’t screaming I know that much. I can’t comment on the hitting tow haul at speed as to what it does as I’ve never done that. Tow haul is on or off right from the get go. However all this was in M mode in 4th gear as it could never tow a 6500 lb trailer in 5th or 6th.
GM Jeff, does it do the same thing at speed if you are in M5?


2013 Sierra SLE 2500HD CC 4wd Z71 6.6 Duramax
 

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I have had the truck since new 25 miles it now has 260,000 miles and this just started . If I’m going say steady 55 miles mph on a level road towing my trailer it will down shift pretty hard and not change until I let off the gas or turn off tow/ haul mode. Turn on tow/haul back on and it will do ok for a few seconds then downshift again .
I wonder if the motor is down on power? Instead of speculating from our chairs, I think it best if you get a Tech-2 on it for proper diagnosis with the shop manual. You can access the troubleshooting guide at AllDataDIY and also check all the TSBs for your rig.
 
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How can you say that . It is UNUSABLE unless I want red line the engine going 55 miles an hour or less.

the t/h is supposed to downshift for braking or to keep speed up when hauling or just driving without trailer . Not rev up 3000 rpm for mo reason. I have driven this truck for 250,000 miles and have put 1,000,000 miles on my other GM trucks with t/h and never had that issue.
Hi Jeff, hoping you’re still on here and maybe found out what was wrong with the truck downshifting while holding a steady speed in tow haul mode as my 08 Sierra 2500hd is doing the same thing at 287,xxx miles
 

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Hi Jeff, hoping you’re still on here and maybe found out what was wrong with the truck downshifting while holding a steady speed in tow haul mode as my 08 Sierra 2500hd is doing the same thing at 287,xxx miles
The problem is that your tranny is on its last legs. The mileage is just too high, and the o-rings are hard as a rock. If you are planning on keeping it have it rebuilt now, before it pukes metal through the pump, and it can be done at your convenience.
 
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