Interesting... progress with odd trans behavior? (2015 6-speed)

Jimmyc! · May 17, 2016

I'm on day one performing this and I can say there is huge difference. I previously had my TCM flashed for relearning. Made no difference. This is like night and day. Thanks OP!

afireinside7444 · May 17, 2016

Been doing this about 2 weeks now everytime i drive. It is much better overall. I notice if i turn it off when on the gas/under load holding steady rpms it feels as if i dropped maybe 200 lbs out of the back of my truck another analogy it feels like you had a sticky brake caliper slowing you down and suddenly frees up.

andyhaug · May 18, 2016

I noticed this in stop and go with stop lights. With it on it feels like I am dragging an anchor, with it off it is much more snappy off the line.

OmniGLH · May 18, 2016

Awesome that this has turned into such a thing! Hopefully SOMEBODY at GM sees this!

My theory, as I've now gone through a few tanks of gas doing it... is that it has mostly to do with the torque converter. Seems like the torque converter stays locked up a lot more with grade braking ON. Which would make sense... can't get grade braking if the converter isn't locked up.

There are days where I forget to disable it, and can usually tell within a few miles that I forgot. Truck lugs, clunky shift, etc.

HiggySTL · May 18, 2016

Been doing this about 2 weeks now everytime i drive. It is much better overall. I notice if i turn it off when on the gas/under load holding steady rpms it feels as if i dropped maybe 200 lbs out of the back of my truck another analogy it feels like you had a sticky brake caliper slowing you down and suddenly frees up.

EXACTLY! I'm on week 2 of shutting it off and I still think it makes a big difference (for the better) in the way it performs.

Unlike others, I haven't noticed any MPG increase though. In fact, I have noticed over the past 2 weeks I have lost about 2 MPGs by turning it off. I don't think that has anything to do with the grade braking though, and has everything to do with me enjoying being able to drive a little more aggressively and having the truck perform as it should.

OmniGLH · May 18, 2016

Do the Tahoe/Yukon have this same issue?

Redray · May 19, 2016

Boy am I glad I saw this thread! Only 1 day and about 60 miles but what a difference, it truly drives like a different truck. If you haven't tried this yet- what are you waiting for?

Drainpipe · May 19, 2016

I'm excited to try this. I thought my only way to get a better shift experience was with a tune!

fondupot · May 19, 2016

I'm excited to try this. I thought my only way to get a better shift experience was with a tune!

Get a tune too. You will be even more happy.

It's basically second nature now to get in the truck, start it up and hold the tow/haul button for 5 seconds. I don't even realize I do it anymore.

99-ls1-ss · May 19, 2016

I wonder if the people that haven't noticed as big of a difference have their trucks leveled? Someone mentioned that the raked stance of the trucks could be confusing the grade braking. That seems logical since I noticed a slight difference and my truck has been leveled. I have some random clunking and the trans-brain-lock when coming to a stop and then taking off before I stop. I have only disabled mine a few times but I can tell a slight difference. The most noticeable change is coasting and going down slight hills. The truck seems to roll/coast much freer than it did. I have seen a slight mileage increase of 1 to 1.5 mpg which I attribute to being able to coast longer and delaying getting back on the gas.

I have a 2016 6.2 w/8-speed and 3.42

Shu · May 19, 2016

I'm leveled and it is a huge improvement. 5.3 6 speed 3:42

fondupot · May 19, 2016

I'm leveled and it is a huge improvement. 5.3 6 speed 3:42

x2. same exact setup.

Donstar · May 19, 2016

I have read several pages of this thread and I see many contributors who would do well with a standard transmission. A standard transmission will shift into the gear you want, when you want, will coast when you want and will greatly help braking when you want! I am going to give this grade braking disable a try but I couldn't resist putting in a plug for the return of being able to opt for a manual transmission!

Drainpipe · May 19, 2016

I have read several pages of this thread and I see many contributors who would do well with a standard transmission. A standard transmission will shift into the gear you want, when you want, will coast when you want and will greatly help braking when you want! I am going to give this grade braking disable a try but I couldn't resist putting in a plug for the return of being able to opt for a manual transmission!

Yeah, that option died a long time ago. I'd love a manual Silvy.

MyakkaLivin · May 23, 2016

So while certainly not as vocal... I do notice occasional odd behavior with the trans and shifting in my 2015 Sierra 1500 SLT.

I was chatting with a friend of mine I know through a local car club, and it turns out he's actually one of the senior techs at a GMC dealer a few towns over. So I've been trying to pay closer attention when the trans does something funny (harsh 2-3 upshift, delayed downshifts, occasional shudders, feels like it gets "stuck" in a lower gear then pops, etc.) and relaying it back to him.

He hit me up the other day and told me to disable grade braking, and let him know how the truck feels.

To disable grade braking, you hold the Tow/Haul button down for a few seconds, then release it. (This is NOT "hill descent control"). You get a popup on the DIC that says it's been disabled.

It definitely makes a difference. I was concerned it was just placebo effect... but he confirmed my observations are what they expect to see. Much smoother shifting. No more "confused" feeling by the trans. No more odd clunks.

He told me "they" think they're narrowing in on the problem. I assume he's talking about GM/factory. Says one of his co-workers (also a tech) is a big truck nerd and has been trying to sort this stuff out with his own truck.

Give it a shot. Let me know if you feel the same thing I do (for my own curiosity's sake).

('15 Sierra,CC,2wd,5.3,6sp) I tried disabling the grade brake but it made absolutely no change. I was damn hopeful that would solve or at least help this lousy transmission. In fact, I don't notice any change in coasting to a stop(?) The rpm's don't drop when coasting like I thought it would. The engine just follows the tranny downshifting until I get to around 15-25 mph then drops to idle. I do get the notification that grade brake is "off" but it doesn't change a thing.