GMC Transmission issues

[Hotflashjr]

I have a 2007 Sierra Denali I bought used a few months ago with 55k on it. Transmission is the 6 speed which I am not at all used to. I think it shifts hard and the dealer told me those transmissions do that when cold. Mine does it when it's cold, but also any other time. No real rhyme or reason to it. I've been keeping track of it now for two weeks and there is not really a pattern. I have had it back 3 times to them and they can't duplicate it. Used tow/haul mode this weekend on a long hilly trip and more issues. Wouldn't shift until 4000 rpm and a few times I think I could have red lined it. I know tow haul mode adjusts shift points but that's not right. Wanted to run at 3000+rpm on the highway going 60-65 mph with two more gears to go. Anyone have the same issue or know anything about this so I can get the dealer to correct it while still under my 12k GM warranty?

 

[Bob]

Shift points are computer controlled and if the 'puter is seeing something it doesn't like (plugged fuel filter, for example) or a misfire, restricted exhaust, etc., etc., shift points will be "off".

Any trouble codes?

 

[acadam20]

I'd try changing the fluid and the filter for the transmission and go from there.

 

[dhermesc]

According to the owners manual the transmission fluid is supposed to be changed every 30K on that truck, more often if you tow with it. Unless you can present proof it has been changed as "suggested" (required to keep warranty) with Dex V1 you're probably SOL on getting warranty service.

If it has been changed you might want to make sure they used the correct fluid. Many of the quick lube places don't keep the latest and greatest fluid in stock that the manuafacturer suggests using.

 

[wisbaker]

On my Ford the Tow/Haul turns the overdrive off and at 55/60 MPH it runs about 3000 rpms. Owner's manual for most of the new stuff will tell you that when towing/hauling you don't use overdrive. The computer is trying to keep the truck in a gear that allows the torque converter clutch to stay locked, if it runs with the converter clutch un locked to much the tranny gets hot and cooks itself....very bad....very expensive

 

[jackinok]

my 99 has the 700r4 transmission in it and it will act like that once in a while for no apparent reason.my transmission guy says its a glitch in the wiring somewhere.not the computer but the wiring harness itself.ive tried to find some kind of rhyme or reason to it but so far ive not found any one thing that seems to trigger it.he cleaned all the connections good and that stopped it for a long time but its started again,so it could be connections getting corroded over time.

 

[Hotflashjr]

It has a tranny temp gauge and I was able to keep it 10-15 degrees cooler in overdrive on the highway by wathcing hills and my driving than by using the tow/haul mode even in the real hilly terrain. It would get up to 160 degrees in tow/haul with little cool down on down hills. In overdrive I could keep it around 138-141 degrees. I also wasn't trying to hold a constant 65 mph and would allow the truck to slow to 60-55 on the hills.

 

[Hotflashjr]

Dealer told me 100K on tranny fluid change. I never looked in the book thinking thats about what they recommend for everything now a days. It now has 60k on it and it has never been changed. I think that is my next step but I am going to change with Amsoil. Meets or exceeds the GM product, is actually a bit cheaper than the GM stuff too.

 

[Hotflashjr]

None. Not a single one. I took my code reader with me and had it plugged in the whole way. Dealer said no trouble codes and if they can't duplicate, no service even though there are 4 service bulletins out for this truck and tranny. I haven't done a fuel filter on it yet but bought it as a GM Certified used, 180 point inspection... so far I'd say that is about worthless!

 

[Hotflashjr]

One of the service bulletins out for this truck/tranny is an electrical connector issue of some sort. I think I am going to change the fluid and while I am under there check all connections, clean'em up, and put dielectric grease on everything.

 

[Bob]

It would be interesting to connect up a high-end scan tool or laptop with tuner software (my son uses HP Tuners) and watch engine load, injector pulse width, MAF, etc., vs. shift points.

(Which reminds me, a goofy MAF sensor can cause wacky shift points. Oil-lubed air filters (example, k&n) spew oil mist into the MAF and make the sensing element collect dust, thermally insulating it and making for flaky air flow ratings from which the computer then (erroneously) calculates engine load and shift points.)
HP Tuners

 

[Bob]

Whole it certainly can't hurt to change the oil, I'm pretty convinced it's an engine performance/ 'puter/electrical issue.


It would be interesting to connect up a high-end scan tool or laptop with tuner software (my son uses HP Tuners) and watch engine load, injector pulse width, MAF, etc., vs. shift points.

Which reminds me, a goofy MAF sensor can cause wacky shift points. Oil-lubed air filters (example, k&n) spew oil mist into the MAF and make the sensing element collect dust, thermally insulating it and making for flaky air flow ratings from which the computer then (erroneously) calculates engine load and shift points.

Any chance your's has been run with one of those #&%* things?

They can be CAREFULLY cleaned and there is "MAF sensor cleaner" on the market.
HP Tuners

 

[dhermesc]

The dealer will tell you anything you want to hear as long as it doesn't cost them money.

We have several Chevy 1500s with the V6 and 4 speed transmission. To keep the warranty you have to follow the "severe duty" maintenance schedule. If you read the details on "severe duty" you'll find just driving your vehicle anywhere on the North American continent qualifies as severe duty. The dealership won't get into those kinds of specifics until it does something they will need to file for reimbursement from GM.

 

[luv2wrench]

I play with the 6L80 transmissions all day at the GM dealer. They have sealing ring issues for the 1-2-3-4/ 3-5-R clutch housings to the 2-6 clutch housing. Causes slippage and neutral when started cold then bang from Park to R or D.
Also see a lot of issues with valve bodies and TCM solnoid packs. Your code reader will probably on read ECM codes, not TCM codes. The TCM is inside (trans computer) the transmission. Changing DExtron 6 fluid before 80-100 K is a waste of money. it is naturally dark in color from rust inhibitors and is fully sythetic. Change every 50 if its a work truck and 8600gvw or bigger.

 

[Bryan inIowa]

Fuel fiter is in the tank ,,serviced with pump replacement

 

[luv2wrench]

The issue with the connector at the trans is dealing with the GM Lan High speed communications. This causes all kinds of codes in all 20 or so modules and is usually fixed by unplugging the trans connector and plugging it back in. This issue causes no movement or only 3rd gear or limited gears up to 3rd or so.

The 6 speeds didn't get all the bugs worked out of them until 2010. And i think they still shift terrible and busy. Give a hesisation feeling too. biggest complaint i get.

 

[luv2wrench]

There is probably 50 service bulletins for this truck that only we can see at the dealer. Give me your VIN and I will check your TCM for software upates.

 

[Hotflashjr]

I put in a new Amsoil air filter when I changed out the engine oil about 1,000 miles ago. It is a dry element filter, not oil like a K&N. I also cleaned my MAF then with the spray stuff. I usually hit the MAF twice a year for good measure.

 

[Hotflashjr]

Do you have an e-mail I can send my vin to?

Dealer mentioned there was no new "updates" last time I was in there.

 

[luv2wrench]

just post vin here.

 

[Hotflashjr]

Having bought the truck used I am not sure how it was run the first 55k miles. Carfax said one owner and it was a local guy, not a company, lease, etc. The dealer I bought it from sold it new and has done the "service" on the truck since new. I was thinking that since I do not know how it was used before with 60k on it now an oil change and filter wouldn't hurt anything if for piece of mind if nothing else.

I get hard shifts from 1-2 randomly doesn't matter what temp. the tranny is at and it doesn't matter if it is an up or down shift. The easier I am on the gas pedal the more you feel the hard shift. It does sometimes shift hard in other gears as well. Haven't noticed any slippage or hesitation but I am going from the 3.5l colorado to a fullsize with the 6.2l V-8. Dealer keeps telling me I am just not used to the 6 speed and that's "how they all are".

 

[dhermesc]

A 2007 would have Dex V from the factory, which is not synthetic. And Dex VI is a synthetic blend.

 

[jackinok]

i think(dont know) that the reason it doesnt show a fault code is because the computer throws the command to work,shift whatever,but it doesnt know the transmission doesnt recieve it, if that makes any sense at all.in other words it gives the command to shift to overdrive or something,but if the transmission doesnt recieve it due to a bad connection the computer cant check it.so it gets sort of in limbo in between high and overdrive.thats the way it was explained to me anyway.

 

[GT65]

It's amazing what a wide range of competentancy can exist between two things that are supposed to do the same thing.(Somewhere today someone is going to have root canal performed by the "WORST" dentist in the "World" doing root canals today.YIKES!!!!!!!!!!)
What I'm getting at is most tuners andsuperchips are fine but some are "crap" that can even hurt your system,especially,if installed wrong.
Sounds like yours might be stuck on "high performance mode" (strong shift points and it doesn't shift till redline?).
This same logic can be used with your GM dealership.That's there job to figure what's wrong with your car and fix it.If they can't do go to another one.
Good luck and I hope no one has a dentist appointment today!

 

[Hotflashjr]

2GTEK638971696375

 

[luv2wrench]

nope. dex 6 was in 2006 and later. trust me. no such thing as dex 5.

 

[luv2wrench]

double check that vin. told me invalid vin.

 

[buickanddeere]

All normal. 5th and 6th are over drives and will see little service when hauling a load. 5th & 6th are for people who own a truck and drive it as a car.
Firm shifts wear the clutch packs less. You may have been used to an old trans that was slipping a bit on each shift.
I re-programmed the VCM on my vehicle to obtain shifts where they were needed. It used to shift into 2nd long before redline in 1st. Used to hunt 1-2-1-2-1-2 on steep hills if below 35mph when the hill started.

 

[Hotflashjr]

Just checked again and thats what is on the plate.

 

[Hotflashjr]

Just checked again and thats what is on the plate.

 

[luv2wrench]

24246755 0000A954 - Use this calibration ONLY if customer complains of poor performance and/or lack of downshifts between 35 and 70 mph.

This is the only cal out there for that trans and that won't help ya. By my experience, 2007 are the worst shift feel. got better in 2008 and 2009. All in the trans cals with the ecm. probably nothing wrong with it. Warranty info shows last in for a door handle and left hub.

you have warranty until 7-13-2012 or 68651 miles with cerfified warranty.

 

[Hotflashjr]

I guess I will start with an oil change. It says Dexron VI in the manual. I am going to put in Amsoil full synthetic. Any tips to get all the old fluid out? Thanks again everyone for all the help.

 

[INCase]

If you've got Dexron VI make sure you get the "ATL" fluid not the ATF.

You may want to flush with AMSOIL's flush product as well.

 

[Tom-NorthCenTX]

You keep saying below that you are going to change the tran to Amsoil yourself. This is the last thing you want to do right now. The tran is under warranty, which you may just screw aroung and lose. Get it fixed first at a competent GM dealer. Then change to whatever you want to risk. Tom

 

[Randy NWMO]

Sounds like it would be worth the time to have it checked at another dealership. Shouldn't cost you anything but time, and maybe the dealer you have been going to doesn't have the best tech working there?

 

[David G]

I believe that transmission calls out a fluid change every 35K, and 25K for severe duty. I would change the fluid if it had never been done. I would not worry about amsoil, just put in what the dealer recommended.

I had that transmission and it was smooth as silk.

 

[dej(Jed)]

My transmission lasted to 80K. Took it to the shop and they said they keep one on the shelf because they change 1 per week. $1500 and I was back on the road. They claimed the factory trany is missing one clutch plate. I am now at 160K and still going strong on this rebuilt trany.