So, whats the fat and skinny on the 6spd GM puts behind the, 6.0 gasse

Spittman · March 26, 2015

With my 1500, manual mode most times could beat out anything that the stock programming would do. The 6.0L and 6L90 combo, GM didn't play CAFE number games with it. The programming and shift points are definitely serious with this setup. Go ahead a try the manual mode, but before you do, use the tow/haul mode so you have a baseline to compare results.

I will absolutely let tow mode do its thing. I don't think I'll be hitting too many big hills anyway. Just that the gauntlet test with the 6.0 Chevy appeared to show the same issues of not downshifting. I'll try to remember to post on here on Monday with a report.

SMiller · March 27, 2015

We have several regular cab Dually's for work with the 6.0. They are used for towing and at roughly 110-130k we blew every single transmission on our 2011 trucks. We thought it might be related to the model year but just this week we had one go on a 2014 at 120k. They have all been well maintained so not sure if this is normal or if there is a problem when they are given heavy use for most of their life. We have a rep out inspecting the 2014 and hope they will step up to assist with the repairs. Up until they went out they worked great..As a personal use vehicle with just occational heavy use, they probably are probably are bullet proof. What GM needs to do is offer the Allison with the 6.0 as an option for those that use these trucks for commercial purposes.

That blows my mind, I managed a fleet (200+) of '11+ 6.0 2500/3500 trucks and never a single drive train issue, these are landscaping trucks that are pulling or pushing their guts out every single mile.

We had some electrical, some brake, and some body issues but the drive train in the '11+ is simply bulletproof.

I would love to hear more about what your pulling and doing with these trucks, no I am not being a smart ass, I really want to know.

Oddly enough GM DOES put the Allison behind the 6.0 in heavy fleet trucks (UPS).

Edited March 27, 2015 by SMiller

CRApex · March 27, 2015

Motors have been great but without exception we lost tranny's on every 2011. We don't have 200 but all 9 lost tranny's around that mileage. We thought it was a 2011 thing but now the 2014 has had the same issue. We tow goosenecks, 5th wheels, travel trailers, boats basically a misc. mix of different type trailers. I've been wondering if the drivers arent using tow/haul mode every time and if that might have something to do with it. On the flip side, we have had no electrical, brake or body issues..

Spittman · March 29, 2015

If you remember, throw some feedback on this thread please. I'm fairly confident that using the manual mode with any degree of skill will result in even better results. I appreciate their mode of testing though, remove as much error as possible from the test and run it purely on the merits of the OEM design and programs.

Well, just arrived in Alabama. Almost 700 miles, with a 10000 Lb trailer I have to say, it is a world of difference from the 1500. It seemed to stay right in the power band. it downshifted right when I would have wanted it to. Got 6.6 mpg, but its a lot of uphill. Ive made this drive before and the mileage will be better heading north.

rocnrol · March 30, 2015

Well, just arrived in Alabama. Almost 700 miles, with a 10000 Lb trailer I have to say, it is a world of difference from the 1500. It seemed to stay right in the power band. it downshifted right when I would have wanted it to. Got 6.6 mpg, but its a lot of uphill. Ive made this drive before and the mileage will be better heading north.

Thanks for the update, the results so far are encouraging! Really happy with the decision to get my new truck so far.

bellacontractingllc · August 27, 2018

Hello, I just joined tonight. I have a post about my 6L90 and 6.0 3500 hd with a service bed. I had it rebuilt 2 weeks ago by gm, under powertrain. They said it would shift funny for a while and I don't know what a while is. It still shifts hard as of a week of being repaired. the truck weighs 13200 or that's what it says on the door anyway. With my tools, I'm at about 14,400. Is this too heavy or too much for the 6L90 stock? If it is, I am trying to understand why the dealer's couple a crew cab 4x4 with a service bed when they know someone will use it for work. If you guys have any ideas or advice I would appreciate it. I can't backtrack and get a diesel with a stronger transmission at this time like the dealers said I should have done. I still owe for my newer truck. Thanks .

ewbldavis · August 27, 2018

My 2015 shifted fairly smoothly when we tugged 8500# TT to South Carolina 2 weeks ago. The grade braking didn't kick in unless I hit brakes - assuming the TT simply isn't heavy enough for the truck to care. We trucked along WV turnpike with ease at about 60-65.

Fancy Gap was a good test on trip home. Pulled a comfortable 60mph @ 4000RPM in 4th I think. This 6-speed is way smoother somehow than the one in my 1500 Sierra (same year, probably same/similar tranny). No complaints here.

sillywillie07 · August 27, 2018

Hello, I just joined tonight. I have a post about my 6L90 and 6.0 3500 hd with a service bed. I had it rebuilt 2 weeks ago by gm, under powertrain. They said it would shift funny for a while and I don't know what a while is. It still shifts hard as of a week of being repaired. the truck weighs 13200 or that's what it says on the door anyway. With my tools, I'm at about 14,400. Is this too heavy or too much for the 6L90 stock? If it is, I am trying to understand why the dealer's couple a crew cab 4x4 with a service bed when they know someone will use it for work. If you guys have any ideas or advice I would appreciate it. I can't backtrack and get a diesel with a stronger transmission at this time like the dealers said I should have done. I still owe for my newer truck. Thanks .

Your truck doesn't weight 13,200. That is the gvwr of the truck. So if the gvwr of your truck is 13,200lbs and it is 14,400lbs then you are over weight by 1,200lbs. That's the max the truck is supposed to be loaded. When they rebuilt it did they reset the transmission shift adapts? If not when they rebuilt it and didn't reset this it can be bad for the trans. It learns how you drive and adapts the shift points to how it is used.

FreeAmerican · September 19, 2018

On 3/26/2015 at 8:59 AM, CRApex said:

We have several regular cab Dually's for work with the 6.0. They are used for towing and at roughly 110-130k we blew every single transmission on our 2011 trucks. We thought it might be related to the model year but just this week we had one go on a 2014 at 120k. They have all been well maintained so not sure if this is normal or if there is a problem when they are given heavy use for most of their life. We have a rep out inspecting the 2014 and hope they will step up to assist with the repairs. Up until they went out they worked great..As a personal use vehicle with just occational heavy use, they probably are probably are bullet proof. What GM needs to do is offer the Allison with the 6.0 as an option for those that use these trucks for commercial purposes.

Agree, didn't GM put the Allison behind the 8.1?

2017HD · September 21, 2018

I had one of the first 6spds in 07. It was a solid transmission and towed my 6000 lb Arctic Fox around for 10 yrs before I traded it for my new DMax. I agree that 4th gear and 3000-4000 RPMs is a sweet spot for towing hills. As far as the tuning goes, I think GM programmed it to not downshift until the RPMs are down in the lower torque band - esp when these engines produce almost 90% of their torque by 2000RPMs.