I wonder if Allison regrets letting GM put their name on these transmissions? I know every brand has their quirks and problems but 900 miles is ridiculous.

 

@ 1967-mustang
Bummer, that sucks.
Any warnings before dying, slipping, searching for gears, or ???

Edit: I've got 2100 miles on mine and I've felt it slipping a few times, not when towing, just around town.

 

No was fine, and then on Good Friday, on our way back from getting Chick-fil-A, it started shuttering no matter what gear or speed. Did not drive it that weekend. On Monday, I tried to drive to work, got about 500 feet out of my neighborhood, and it felt like someone rear-ended me. Turned around to dive back home. Had it towed to the dealer.

 

18,000 on mine, mostly towing, and no issues.

 

I hope they can get the trans swapped quickly, depending on when GM can get one to the dealer. I would really like to keep this truck. Other than the trans issues, I like it. This is my first GM product in about 30 years and my first 3/4 ton. My expedition just was not up to the task of pulling my boat every weekend to the lake and back, about an hour each way. Really liked the looks of the GMC HD compared to the Ford Super Duty

 

Good luck, just got my truck back after a 5 week wait due to a valve body failure. Call GM and open a case number, tell them you use the truck for income that may help.

 

How do I find a number for GM?

 

Only time will tell…

Well that’s kind of a crappy way to look at it. Think it’s unlikely I’ll have issues. Far as I know I run a truck as hard or harder than anyone here. 🤷‍♂️

Pay no mind to @BoiseRob, he’s just jealous he doesn’t have a new truck with the 10 speed that tows and drives so much better than his truck. He’ll say he isn’t, but it’s obvious by his comments.

 

Sad !! Wow

 

Man now I'm worried , my trans since new has shifted funny mainly when it's cold , when I'm towing my toy hauler it seems to shift fine , mine is a 2024 3500 Denali Ultimate nicest truck I have ever owned, but I really liked my 6 speed in my 2018 HD much better , I feel a recall coming

 

I hear you. My 2025 does funny things when cold especially going around slow corners, no problems when towing or warm.
My 2007.5 true Allison 6 speed was rock solid and never had the slightest problem... also was easier to check fluid level, change spin on filter, and drop the pan.

 

It’s sad that the new trucks are having issues with the Allison transmissions now. Before GM got full control of them, they were the talk of the town for reliability and strength.
I baby my LML engine to ensure the pump stays happy. Have 205k plus on her now, and hoping to at least double that without issues. Don’t get me wrong, I use my truck for what it’s intended to be used for and has been reliable. Sure I would love to have a new truck with more bells and whistles, but cost and reliability makes me stay in my current truck without looking back.
Hope you get your truck back soon without further issues.

 

It’s sad that the new trucks are having issues with the Allison transmissions now. Before GM got full control of them, they were the talk of the town for reliability and strength.
I baby my LML engine to ensure the pump stays happy. Have 205k plus on her now, and hoping to at least double that without issues. Don’t get me wrong, I use my truck for what it’s intended to be used for and has been reliable. Sure I would love to have a new truck with more bells and whistles, but cost and reliability makes me stay in my current truck without looking back.
Hope you get your truck back soon without further issues.

It’s sad that the new trucks are having issues with the Allison transmissions now. Before GM got full control of them, they were the talk of the town for reliability and strength.
I baby my LML engine to ensure the pump stays happy. Have 205k plus on her now, and hoping to at least double that without issues. Don’t get me wrong, I use my truck for what it’s intended to be used for and has been reliable. Sure I would love to have a new truck with more bells and whistles, but cost and reliability makes me stay in my current truck without looking back.
Hope you get your truck back soon without further issues.

Ford is having issues with their 10 speed transmissions also, I was told Ford and GM worked together on the engineering of these 10 speed transmissions. Not sure why?

 

Ford and GM worked together on transmissions from 2013 to 2017, 9 and 10 speed models.

 

I thought GM said the 2025 transmissions in their vehicles are fine, "no problems" ... no recall actions required or issues, etc.; read the commentary from GM Authority. Until GM comes clean on what the exact problem was, and exactly what they did to fix it, GM is going to have a credibility problem.

 

Love my 2021 2500HD and especially the transmission. 80k on it, about half towing. No trans issues but it's getting a new engine due to the lifter coming apart. Been without it a month now with no way to pull my FW or gooseneck trailers. Hopefully the tech does a good job and truck will be as good as new.

 

I need a towing capable truck.... when is GM going to get "stuff" together. The L87/6.2L V-8 gas engine has its "lock up" issues, crankshaft/connecting rod alignment wear failures.... and this 10 speed "Allison" transmission problem. One would believe these light/medium duty trucks are major contributors to GM's profit and cash generating ability. My understanding is that GM won't let any of these "failed cores" into the market for a 3rd party analysis, hence it is difficult to determine what the real cause for these failures. Increasing the lubrication oil weight seems like a deferral and time delay strategy, not a fix, per se? 'Craig' I though the lifter issue was "fixed" when GM went to the dynamic AFM system to randomize the firing of the 4 firing cylinders rather than the just the static AFM, the prior generation of L86 engines, i.e., same 4 firing cylinders? Perhaps I'm recalling this incorrectly?

 

.... Craig...OH, the lifter problem was in a Duramax engine.... sorry my confusion....

 

GM Flint Truck Plant that builds the 2500 and 3500 Chevrolet and GMC trucks is parking THOUSANDS of the trucks in massive storage spaces around Genesee county Michigan. I would think its a major quality reliability issues going on, I don't know what the issue is,,Hmmm I hope its not the Allison trans.They have been doing this for over a month now,a 40 acre lot 5 miles from me is full,GM has several areas this size or bigger stuffed with new trucks fresh off the assembly line.

 

It says Allison on the hood but it's not an Allison,, sad but true.

 

Interesting about the 'storage space' holding lots; that does sound like an issue.... can you imagine what that does to cash flow? ... I'm an ex-auto financial executive from Monroe Auto Equip... down the road.....Tenneco Automotive. Regarding problems with GM trucks, you can take your pick, L87s or Allison transmissions????

 

My 2012 LML has been very reliable as far as engine and transmission. The transmission has never given me any issues not even single slip. A lot of LML haters out there but they are rock solid if you take care of the cp4 issue. They can burn up to B20, first year with exhaust brake and the engine is rated one of the best pick up diesels made. I recommend a coolant filter with Amsoil HD coolant, noticed a drop in running temps and good for 8 years. The transmission is a dream. I hear about a lot of issues with the 10 speed , I’ll stick with the true Allison 6

 

After 5 weeks of being down I finally got my truck back with the new valve body. Seems to be shifting as it should but I haven't towed anything yet. I'm going to start looking for an older southern truck with no rust, while the new trucks are a pleasure to drive there is way too much going on with all the emissions and electrical.

 

I =so= wanted to drop an LBZ into my '02 2500, but the interior was shot, so it wouldn't have been worth it.

 

2023 High Country Duramax: probably owned/drove 15+ 3/4 tons (all GM) in my life (73 yr old Colo. construction owner). Bought this truck one yr old with 12K; now 32 K and 90+ % towing my 14K lb 5th wheel camper. This HC is the most powerful, plushest, nicest truck I've ever owned and love it. No issues at all and use cruise up from Denver over the Rockies (6 times so far) and engine brake downhill- all on cruise=love it. Of course, now that I've said that, something will probably fail.

 

Pop off the intercooler as well as the intake horn although I find it easier to view the horn side by sending a camera through the horn from where it connects to the air filter instead of removing the horn which is a bit of a bear. Hope this helps

 

I have a 2023 3500, since the day I picked it up it had trans issues that I immediately complained about, and that the dealer told me was everything from a tight clutch pack to an update to a wire harness they had every excuse why in park at idle it would lurch forward randomly and make a banging noise, nothing they did ever fixed it. Then at 28,000 at idle in park in a grocery store parking lot, the transmission blew up, fluid just started pouring from the bell housing and it kept making a slamming sound, I immediately drove it across the street to the dealer(oil slick is still there), and now this time -yea trans is blown.. I waited 3 months for it to be fixed having to make the payment the whole time, I was not offered a loner, as they said GM doesn’t do loaner cars, but I could rent, and they would reimburse(still waiting for that reimbursement) then I was told its taking so long because the mechanics quit, so several different mechanics worked on it, they said they have no one available that knows how to work on these trucks, and had to wait for an outside technician, then they told me they were reusing some parts from the old trans, namely the old filter.. gm dosnt cover the filter or pan and some other housing, so I had to pay $230 extra for a new filter, because I thought that would make sense, why in the world would you reuse a filter from a blown trans? Got it back and it was fine, much better than before no lurching slamming, was good to go.. but wait not so fast, now at 62,000mi its been doing the same thing in park, started doing it randomly and lightly, now its getting to be a harder slam and lurch at park at idle, even sometimes doing it in drive while at a stop, I have called the dealer, and same thing- its normal- its an update- wire harness- low fluid,.. BS this transmission is absolutely garbage to which GM is never going to stand behind. This trans was never tested fully before it was implemented or they knew the design flaws and went ahead anyway because thats what huge corporations do, they just are greedy b()$@“:/ds, they dont care if you bought their garbage, and wont stand behind it.. boy do I feel like a sucker.

 

Last Friday, my GMC dealer installed a new transmission with the updated valve body in my truck and returned it to me. So far, so good. Drove it over the weekend, and everything appears to be fine. The service manager said they have not had any transmission issues with customers' trucks after installing the updated valve body. Will tow the boat in a few weeks. All in the truck was down for 4 weeks waiting on a new trans from GM.

Thanks, Bratwurzt666, for the advice on calling GM. I did find a number for lemon law issues for GM. I opened a case, and I think that is what got things moving in the right direction.

Here is the website.

Site Maintenance

 

Last Friday, my GMC dealer installed a new transmission with the updated valve body in my truck and returned it to me. So far, so good. Drove it over the weekend, and everything appears to be fine. The service manager said they have not had any transmission issues with customers' trucks after installing the updated valve body. Will tow the boat in a few weeks. All in the truck was down for 4 weeks waiting on a new trans from GM.

Thanks, Bratwurzt666, for the advice on calling GM. I did find a number for lemon law issues for GM. I opened a case, and I think that is what got things moving in the right direction.

Here is the website.

Site Maintenance

Hope everything works out for you now without any more problems. Keep us posted on how your truck performs.

 

Has anyone installed an aftermarket Valve Body? Came across this interesting video (no affiliation). They mention both the "Allison" and the Ford 10-speed.

 

I have a 2023 GMC Sierra HD3500 6.6 Duramax. March of 2025 the valve body failed after 23,000 miles, which around 6,000 miles was hauling 3,000lbs, no more. The failure happened when the transmission had an extremely hard shift at 55 mph and then went into 5 gear limp mode. Computer through code P0700 and P0747. The P0747 is the code that tells you the valve body failed. When I took the truck to the dealer, they would not let me take the truck home because of the high risk of the transmission locking up and causing bodily injury, aka crash. Since the valve body was back ordered, I was warmed that it may be a month to get a replacement and install it. I finally got the truck back after 33 days. To add to the frustration, GM would not give me a loaner truck. They would give me a loaner SUV but that did not have what I needed out of a vehicle. I bought a truck for its utility. I already have an SUV. This was the first GM product I have bought in decades and regret the decision. I am still hoping GM decides to extend the coverage of this faux Allison transmission.

 

I have a 23 2500 AT4, with I similar experiences towing. Taking my small trailer back from Sonora CA on Hwy 88 about Jackson Rancheria, I had two hard shifts and then went into limp mode. Did not know about resetting the system, so I waited for a tow truck and got a tow home for both trailer and truck. At 41000 miles after 60 days without my truck I talked with the part guy looking for a status on the valve body. He said he had a transmission at the dealership and after a few days got approval to install the new transmission. You would think that fixed the problem, but no. Still shifting badly. The dealer reflashed the TCM checked the fluid and off I went again. Seemed to work for a while but it started shifting badly again. Not as bad but still an issue. Took it in again at 51k and they found the transmission had two quarts to much and then re learned the TCM. Seemed to work but after about another 1500 miles the downhill coast shifting problem has returned. Not solution as yet.

 

Tell me about your 'downhill coast shifting problem'. A couple of times my 2025 2500 has shifted down on a moderate grade with no action by me. On one of those time, I was having difficulty getting it to upshft after the grade, like it was stuck in the lower gear. Your observations?

 

Depending upon how you interpret the scenario, this would be "normal" behavior for this truck. In D the downshift on desscent is very aggresive and there is a considerable delay in upshifting. There are several threads about this, I just operate mine in Manual Mode and bump it to 10, it still may downshift, but not as many gears on a descent. It is especially annoying that it takes so long to upshift after the programmed downshift.

https://www.duramaxforum.com/threads/arrggh-that-dreaded-downshit-and-delayed-upshift-after-going-downhill.1024143/?post_id=12468026#post-12468026

and

https://www.duramaxforum.com/threads/my-allison-is-trying-to-kill-me-multiple-downshifts-while-towing.1037974/?post_id=12626172#post-12626172