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Old     (jonblarc7)      Join Date: Jul 2006       09-06-2016, 8:20 AM Reply   
I pull a supra 24V

Last couple trips my 2008 Denali with 6.2 will drop two gears and red line with no warning. This is on flat ground going around 45-50 mph.

Today I pull out on the main road about a mile from my house. I notice it's running at about 3200 RPMs and not up shifting that last time down to about 2200 RPMs. Next thing I know it drops two gears and red lines. So I take it out of two haul mode and it's fine. So I put back in TH and it does the same thing. So I drive to the lake in M and just select the gear I want and it shifts fine, This was a 15 mins trip to the lake.

We go out all day and I load the boat up to come home. This time I put in TH and head home down the highway at 75 mph and it's fine. Then I get off the highway close to the house on some back country roads and it does it again.

Anybody have any idea's
Old     (granddaddy53)      Join Date: Dec 2013       09-06-2016, 9:28 AM Reply   
Quote:
Originally Posted by jonblarc7 View Post
I pull a supra 24V

Last couple trips my 2008 Denali with 6.2 will drop two gears and red line with no warning. This is on flat ground going around 45-50 mph.

Today I pull out on the main road about a mile from my house. I notice it's running at about 3200 RPMs and not up shifting that last time down to about 2200 RPMs. Next thing I know it drops two gears and red lines. So I take it out of two haul mode and it's fine. So I put back in TH and it does the same thing. So I drive to the lake in M and just select the gear I want and it shifts fine, This was a 15 mins trip to the lake.

We go out all day and I load the boat up to come home. This time I put in TH and head home down the highway at 75 mph and it's fine. Then I get off the highway close to the house on some back country roads and it does it again.

Anybody have any idea's
I ruined a trannie in my 2000 ram not using "OD off" switch, old equivalent to tow haul. I Read the manual in its entirety before towing Mine simply puts it 3rd gear, dropping two gears yours sounds like a 5 speed or a highly modified computer program allowing the use of 4th gear OD in tow haul.
The OD gears are orbitals that should not be used for towing where gear changes are occurring. Select 3rd gear, accept your gas mileage and save your transmission ,

It us exactly the high speed under load down shifting that will ruin it
Old     (jonblarc7)      Join Date: Jul 2006       09-06-2016, 10:19 AM Reply   
I have the 6 speed and it used to tow great. And at 2200 rpm at 60 is 5th gear. It rarely goes into 6, the problem is when it's acting up it's not making it into 5th. So it will be in fourth at 3200 rpms and then drop two gears to second at 50 mph which is like 5000 rpms or more. I don't really look at this point because I'm try to not blow the engine up so I'm switching TH off or trying to put it in manual mode. This is on flat land or maybe a slight bump in the road not a hill it shouldn't be down shifting at all.
Old     (granddaddy53)      Join Date: Dec 2013       09-06-2016, 10:35 AM Reply   
2200 at 60 is very economical , economy is not the goal of towing a large load. If manual actions like that are necessary during operation to avoid a probkem, there is a problem , find out which of the gears is not high speed performance or OD and put it there. My old gas guzzling bad ass tow machine is 2000 at 50 in 3rd, 2500-2600 st 60-62, bad mileage , no tranny issues , and if you start up a huge bridge in 3rd at 60+, at the top with no shifting if you know how to feather the accelerator , your speed will end up at 49+ with no gear changes , I'm ok with that on a busy 3 lane very tall overpass with no shoulders on an interstate towing a boat . I don't need to go 65 over a bridge , nor would I want to hear those rpms in my old motor. Back when I burned up the tranny I flew to the fishing hole snd was crazy enough to tow 65-75 with no trailer brakes to get to a fishing hole 90+ miles of road and water by 6:am. Got smart and ran out of my extended truck warranty so I changed to low and slow just like the boat in water

Last edited by granddaddy53; 09-06-2016 at 10:37 AM.
Old     (granddaddy53)      Join Date: Dec 2013       09-06-2016, 10:46 AM Reply   
Quote:
Originally Posted by jonblarc7 View Post
I have the 6 speed and it used to tow great. And at 2200 rpm at 60 is 5th gear. It rarely goes into 6, the problem is when it's acting up it's not making it into 5th. So it will be in fourth at 3200 rpms and then drop two gears to second at 50 mph which is like 5000 rpms or more. I don't really look at this point because I'm try to not blow the engine up so I'm switching TH off or trying to put it in manual mode. This is on flat land or maybe a slight bump in the road not a hill it shouldn't be down shifting at all.
I have to break off cruise control depending on hill I know that are smaller or larger as cruise control only knows one way to deal with load which is to downshift , so cruise over certain hills is a no no. When it does happen cause of cruise, cause I'm in 3rd I'm downshifting to 2nd which is an acceleration or load gear, so trannie ok, now it's the rpms in the motor and I've never seen my rev limiter hit either when cruise down shifted from 3 to 2
Old     (07launch22ssv)      Join Date: Feb 2007       09-06-2016, 11:00 AM Reply   
I know that my 2007 Denali likes to downshift when slowing down, think engine breaking. I tow quite a bit around town and rarely use my TH because it just seems like it shifts too much.
Old     (jonblarc7)      Join Date: Jul 2006       09-06-2016, 11:07 AM Reply   
It's not dropping because of a hill this is just randomly on flat ground. On the way yesterday it worked perfectly for 11 min of a 15 min trip. Then after making a right on a long flat road take might even be slightly down hill. I notice it hadn't made it's last shift then bam it drop 2 gears for no reason. I was already up to speed and cruising on a flat road. It should be commanding a down shift and especially not 2 down shifts!!!!
Old     (jonblarc7)      Join Date: Jul 2006       09-06-2016, 11:11 AM Reply   
I'm thinking its a speed sensor that is on its way out or something. Because its' like it doesn't know what to do it so just drops gears like it slow down or engine breaking but I'm not try to stop.

The to gear drop is bad enough to throw things in the floor.

It's not normal. Until this started happening I would say the 6.2 pull almost as good as my duramax did.
Old     (CALIV210)      Join Date: Jun 2015       09-06-2016, 12:12 PM Reply   
Tow haul mode on the Allison locks up the torque converter to keep it from building excessive heat and also downs shifts when braking its does not lock out overdrive . You should really be over on the Duramax forum asking these questions you will get a lot more help there . In my experience the Allison is pretty bullet proof unless you throw a ton of added horsepower at it . If your truck is programmed you might try putting it back to stock and then seeing how it reacts .
Old     (CALIV210)      Join Date: Jun 2015       09-06-2016, 12:20 PM Reply   
heres a good read ..


Allison Tow/Haul Mode Explained
12-22-2015, 12:42 PM
What happens when you activate the Tow/Haul button?

You already know that heavy duty diesel trucks are ideal for towing but you might not know what Tow/Haul mode is or how it works. Using this mode properly can improve your towing experience and you might even like the way it affects your daily driving.

Tow/Haul Mode Explained…

Beginning in 2001 with the Duramax engine and Allison transmission combo in GM trucks, GM included a new feature called Tow/Haul. You can activate this feature by pressing the button at the end of the shift lever to make the towing process more enjoyable and safer.

When the Tow/Haul mode is engaged a few things happen.

The shift pattern of your truck changes. The lockup of the torque converter happens at a lower RPM and it applies a much more aggressive downshift pattern when the brakes are engaged.

With tow/haul mode engaged, this tells the TCM (transmission control module) that the shift patterns need to be changed. Generally it will raise all of your part throttle shifting by 300-400 rpms. This will help keep the engine up higher in its power band when a shift is completed and improve acceleration when towing a heavy load.
With tow/haul mode engaged the torque converter will lock much sooner. Normally, the TC (torque converter) will lock in either 4th or 5th gear at around 50mph. With tow/haul engaged, the TC will lock in 2nd gear at about 25mph.

What’s the benefit?

Once locked up, all of the engine power will be passed through the transmission instead of being lost by the TC when it is only using fluid coupling to transfer power. You will notice more responsive acceleration and it will help to keep the transmission fluid cooler.

With the tow haul mode engaged, downshifting will be much more aggressive during hard braking. With a heavy trailer, this can give you more stopping power.
When going down a steep grade with tow/haul engaged, you can tap the brakes quickly a couple of times to get the truck to downshift and use engine compression to help slow the truck. The engine can rev as high a 4000rpm when this happens, to help slow the truck.

To get the truck to shift into a higher gear once deceleration is no longer needed, just apply the accelerator to gain speed and shift into the correct gear for cruising.
There are a few instances owners have found where they prefer normal mode to tow/haul when towing. One of those is when towing a load up a steep grade where your speed is limited to 35mph or less. By staying out of tow/haul mode, the truck can remain at a higher rpm to keep power up and EGT’s down. The “trade off” is your transmission temperatures will rise more quickly than if the TC was locked.

Tow/Haul mode isn’t exclusive to towing a trailer. It can be used in normal driving conditions. Many people prefer how the truck shifts in tow/haul mode, more so with a built transmission and tuning such as EFI Live, but even the stock Allison owners experience quicker acceleration, more responsive throttle and better shifting when Tow/haul mod is activated during city driving conditions.
Old     (boardjnky4)      Join Date: Dec 2011       09-06-2016, 12:28 PM Reply   
The above discussion is regarding a 6.2L Gas motor, so it doesn't have an allison transmission.
Old     (jonblarc7)      Join Date: Jul 2006       09-06-2016, 12:29 PM Reply   
Good read but this is not an Allison this is the 6l80e in a 1500 denali with the 6.2 V8.

I put long tube headers and a custom tune on it over a year 1-1/2 ago but it hasn't had this problem until the last couple trips. Good idea about post over on the duramax forum though. I know a lot of them are GM mechanics
Old     (patrick232)      Join Date: Aug 2008       09-06-2016, 5:29 PM Reply   
My 09 1500 Chevy with the 6.2 would do this or just not shift until the throttle was lifted or hammered. In the 75k I had it it would do it a handful of times on flat ground and could never reproduce. Haven't seen it with or 13 or 16 Suburban with the 5.3 or 15 duramax.
Old     (jonblarc7)      Join Date: Jul 2006       09-07-2016, 5:29 AM Reply   
Patrick mine has always done that too sometime it just does want to shift so in the past I would take it out of TH let shift then put it right back in TH. But this is different

I'll try and take a video of it doing it this weekend when I pull the boat to the lake.
Old     (CALIV210)      Join Date: Jun 2015       09-07-2016, 8:52 AM Reply   
Quote:
Originally Posted by jonblarc7 View Post
Good read but this is not an Allison this is the 6l80e in a 1500 denali with the 6.2 V8.

I put long tube headers and a custom tune on it over a year 1-1/2 ago but it hasn't had this problem until the last couple trips. Good idea about post over on the duramax forum though. I know a lot of them are GM mechanics

Oh crap I'm sorry I thought it was a Dmax . I hope you get it sorted out soon
Old     (jonblarc7)      Join Date: Jul 2006       09-07-2016, 8:57 AM Reply   
No big deal, I'm going to see if I can just drag the boat over to the tuners house and see if I can log something on HP tuners. Maybe the tune needs to be reflashed or something.
Old     (smuurph84)      Join Date: Oct 2008       10-10-2016, 1:07 PM Reply   
I had the same issues with mine and they chased it for ever. turns out it was a bad battery wire.

have them check it.


note mine would randomly shift even while not towing as well. ( downshifting locking up the tires!)

very dangerous!
Old     (denverd1)      Join Date: May 2004 Location: Tyler       10-12-2016, 12:39 PM Reply   
sounds to me like the some speed sensing parts in trans are either shorting or going out. The tune probably makes matters worse as it likely changed shift points. Would be easy to restore to stock or a milder tune to see if it has any effect
Old     (jonblarc7)      Join Date: Jul 2006       10-12-2016, 1:43 PM Reply   
I'm going to have the trans tune reset next week. I've just been towing it in Manuel mode and it been fine, it's just pain to remember to tap the button all the time to change gears. First world problem though.

If that doesn't work there is a speed sensor that's about 40 bucks that I will try next.
Old     (jonblarc7)      Join Date: Jul 2006       10-12-2016, 1:44 PM Reply   
I meant Throttle Position Sensor

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