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Hey all, recently purchased my diesel Colorado LT with 29K on it. Was previously leased and is in great condition. Only issue I have noticed (so far) is that when it’s first driven the transmission slips for a half a second going into 4th gear at about 30mph on flat ground (no load).
Doesn’t seem to do it again after that. Anybody else experience similar? Thanks!
 

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Hm, mine was recently just fixed for a 3-4 gear shift problem. Mine was clunking/momentarily binding. They tried the fast adapt reset, a PC solenoid and TCM to no avial . And finally Ended up tearing down the whole transmission. Found dirt (from original assembly)and damage in the clutch piston seals, replaced all trans seals and cleaned transmission . Put it back together and resetup the TCM. No problems since.
 

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Hm, mine was recently just fixed for a 3-4 gear shift problem. Mine was clunking/momentarily binding. They tried the fast adapt reset, a PC solenoid and TCM to no avial . And finally Ended up tearing down the whole transmission. Found dirt (from original assembly)and damage in the clutch piston seals, replaced all trans seals and cleaned transmission . Put it back together and resetup the TCM. No problems since.
Mine is at 51000 miles
 

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Mine had a "dipsy doodle" shift at 3rd to 4th. A trans tune fixed it, now it shifts crisply in every gear.

I do think the tolerances of the transmissions vary and some shift a little softer than others. It is probably just that, and nothing really to worry about. The settings in the trans control module sure do dictate how the trans behaves. It is a pity that any sort of tuning, even just transmission tuning, is now out the window in the US.
 

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Mine had a "dipsy doodle" shift at 3rd to 4th. A trans tune fixed it, now it shifts crisply in every gear.

I do think the tolerances of the transmissions vary and some shift a little softer than others. It is probably just that, and nothing really to worry about. The settings in the trans control module sure do dictate how the trans behaves. It is a pity that any sort of tuning, even just transmission tuning, is now out the window in the US.
You cant get an aftermarket tune or something?
 

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I have this same issue. It only seems to happen when running cold, and it has been present since about 10K miles on the vehicle. Now have 51K miles. I was told that this is "normal". Also, note that trans fluid change at 40K made this much less noticeable. I do have the truck tuned with DuramaxTuner engine and transmission files, but the truck does the same thing on stock software.
 

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Discussion Starter #7
I have this same issue. It only seems to happen when running cold, and it has been present since about 10K miles on the vehicle. Now have 51K miles. I was told that this is "normal". Also, note that trans fluid change at 40K made this much less noticeable. I do have the truck tuned with DuramaxTuner engine and transmission files, but the truck does the same thing on stock software.
Thanks for the reply. I don’t quite understand though. It has the same issue with or without the transmission tune?
 

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Mine had a "dipsy doodle" shift at 3rd to 4th. A trans tune fixed it, now it shifts crisply in every gear.

I do think the tolerances of the transmissions vary and some shift a little softer than others. It is probably just that, and nothing really to worry about. The settings in the trans control module sure do dictate how the trans behaves. It is a pity that any sort of tuning, even just transmission tuning, is now out the window in the US.
Thanks for your reply! Was it the Duramaxtuner.com transmission tune?
 

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Thanks for your reply! Was it the Duramaxtuner.com transmission tune?
GDE. They have a few different iterations on their trans tune. In my truck the initial versions took the "firm it up" thing a little too far - it was a little dump truck like, bumping into 1st gear coming to a stop. Nothing scary, just notable. Later versions were really good, and the final version is dead on perfect. It was interesting to run the various calibrations as they really affect the transmission's behavior.

My editorial comment on the transmission settings is this: It does seem that individual transmissions vary in their "tolerances" and tighter settings that approach more optimal running which are perfect in one unit may be a little rough in another tighter tolerance unit. GM's trans settings do not attempt to be "optimal" in any way, they are "safely mushy". That way everybody will have varying levels of slip and flare, but nobody will possibly have rough shifting. There is a lot left on the table as a result, but I suppose this strategy makes sense from GM's perspective.

My main disappointment with GMs settings, aside from the excessive slip, is the shift points rev the engine more than needed. It feels like a lot of the good diesel grunt gets lost along the way. A good firm but not rough upshift just past the torque peak of 2K RPM while accelerating at a brisk but not full on pace is very satisfying, as the truck punts ahead so nicely with such an economy of effort from the engine. Would love to have well set up 10 speed trans with this engine as that would keep the RPM right in the sweet spot, but the optimized 6 speed is pretty decent, if a bit gappy for our engine's narrow rev range.

The one fly in the pie (for me) in all this is the trans holds onto 6th a bit longer than I would like - I don't put much of a load on the motor below 1,500 RPM as I think it loads the rods/crank, etc. If stuck in traffic that wants to go 52 mph (the problem speed) I put it in manual mode and run 5th gear. "Spin to win" I say. The more these things run around 1,800 RPM the better - it is just so happy there :cool:
 

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Thanks again! Great “editorial” and info! ??
I have a 1300 mile road trip this week so it will give me more time to feel it out. She’s my first diesel so it’s been an interesting and enjoyable learning experience so far...I only have about 1500 miles in the seat so far.
 

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To clarify, the 3rd to 4th gear slip that was quite prominent in my truck with the stock settings completely went away with any version of the trans calibrations I have run, it shifts smoothly but firmly into each and every gear, no fooling around. It will delay the shifts and slip a little bit when really cold, like 30 degrees or less out, that goes away once the trans fluid temp comes up over 100F or so on the DIC.
 

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Interesting, that yours flares. My would bang or clunk into gear (3-4) untill they fixed it. Now it no longer bangs, but still shifts firm with no flare. My trans you can tell when the torque converter locks too, firm with no bang. All stock programing. I find the stock diesel trans tune shifts are firmer then it's gas counter parts. Considering the higher torque that's good.
 

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Interesting, that yours flares. My would bang or clunk into gear (3-4) untill they fixed it. Now it no longer bangs, but still shifts firm with no flare. My trans you can tell when the torque converter locks too, firm with no bang. All stock programing. I find the stock diesel trans tune shifts are firmer then it's gas counter parts. Considering the higher torque that's good.
Mine is very smooth too. It's smoother than the "fake shifts" in my wife's 2019 Outback. The only exception is the first shift when cold.
 
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