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  1. #11
    Jr. Mechanic GrizzlyTN's Avatar
    Join Date
    Jun 2010
    Location
    Jackson Tennessee
    Posts
    130

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    Evan has been following the issue, man I can't believe that they could legally call it normal operating. It has pushed my truck into a lady (just a bump and she let me go) and sometimes 2 feet after I've stopped and you can hear the tranny shifting down. But this GM piece of paper says this is normal......

    It's not safe
    2012 Chevy Silverado Z71 4x4 5.3
    Rough Country 2.5' Lift/Level
    Chevy 18's on Toyo Open Country MT 33's
    DiabloSport Trinity Tuner with Custom Tune from Lew
    Debating on AMP Research Powersteps

    2008 GMC Sierra WT 4x2 4.3

    3" Rough Country Suspension Lift w/Control Arms
    Super 44 Flowmaster Straight Dual Exhaust from the Cat Back with 18" Chrome 3.5" Exhaust Tips.
    Moto Wheels 951 18" on Nitto Mud Grappler 33's
    Infinity Kappa Perfect 6.1 System with Kenwood 5.1 amp using Stock Headunit.

  2. #12

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    Can you enact the lemon law? What did the GM customer rep say? Sounds like you need a new tranny.

  3. #13
    Jr. Mechanic GrizzlyTN's Avatar
    Join Date
    Jun 2010
    Location
    Jackson Tennessee
    Posts
    130

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    District GM rep called, told me that my truck is doing what it's supposed to be doing. The things I am complaining about are specified in the GM letter and is functioning properly!!! She said I could write a letter to a PO Box and complain but there was nothing they could do at this time. I asked her why did she bother calling me if she's just gonna tell me what the dealership already said.

    It's still pushing the truck forward after I stop or nearly stop. I guess it's going to take someone having a wreck or God forbid being hurt or killed before they address it as a real issue and not a normal thing.
    2012 Chevy Silverado Z71 4x4 5.3
    Rough Country 2.5' Lift/Level
    Chevy 18's on Toyo Open Country MT 33's
    DiabloSport Trinity Tuner with Custom Tune from Lew
    Debating on AMP Research Powersteps

    2008 GMC Sierra WT 4x2 4.3

    3" Rough Country Suspension Lift w/Control Arms
    Super 44 Flowmaster Straight Dual Exhaust from the Cat Back with 18" Chrome 3.5" Exhaust Tips.
    Moto Wheels 951 18" on Nitto Mud Grappler 33's
    Infinity Kappa Perfect 6.1 System with Kenwood 5.1 amp using Stock Headunit.

  4. #14
    Sr. Engineer
    Join Date
    Oct 2010
    Location
    Indianapolis, In
    Posts
    487

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    From all the posts about this, I would not think the transmision is at all the cause. Sounds more like a realy fast idle condition and when coming to a stop it is just down shifting and the lower gear is allowing the truck to do what it is asked to do and that is to keep moving. Is this a drive by wire? Maybe you take your foot off the gas but the computer doesn't?
    2000 GMC YUKON SLT, 5.3L tow pkg, G80 rear/w 3.73 gear

  5. #15
    Sr. Apprentice
    Join Date
    May 2012
    Location
    Corpus Christi
    Posts
    30

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    Not sure about your sudden stop issue regarding the lunging forward of the truck ,but the delay your are experiencing when romping down on it and then the sudden grab after a few seconds is most likely the torque management that GM has incorporated on all of their trucks to discourage aggressive driving in order to protect the drivetrain components. You can get a programmer and install a tune that will remove about 75% of that feature as well as increase overall performance. Of course it could compromise your warranty ,but what has your warranty done for you so far? I'm surprised that your dealer rep or GM hasn't apprised you that your truck has this torque management feature within the programming of the TCM/transmission control module instead of just saying that it is operating as designed. As for the lunging forward and downshifting issues when coming to a stop,I'm not clear form your post just how sudden of a stop you refer to or if it behaves this way when just coming to a normal stop.Try driving it in M5 mode and see if she behaves the same. This will prevent AFM feature from initiating and you can see if it has any effect on your symptoms.You can safely operate the truck in M5 up to freeway speeds without running excessive rpms.

    Edit: Also try disabling the traction control/stabilitrac by holding the button in for several seconds until the indicator shows both are off.See if this helps decrease the lag time during quick acceleration. I doubt it will from a dead stop but it should improve a rolling quick acceleration scenario.
    Last edited by O'Brien; 12-07-2012 at 06:57 AM.
    2012 silver ice metallic Silverado CC 4X4 /6.2L / 373/9.5" rear max trailering package/ 18" Z71 rims with 285/65/18 BFG TA/KO Ebony leather interior / 2011 grill insert with black mesh/rear fender liners and bed rail protectors/ Z71 skid plates/GM bed mat/2" billet aluminum under strut front leveling kit

  6. #16

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    Hey, I'm a new member from MS. I bought a used truck (08 Sierra) from Serra in Jackson, Tn a couple of months ago. It's spark knocking like a bastard right now, but that's a different thread. Mine has the 4 speed. I test drove an 09 silverado with a 6 spd after I bought mine (thinking about unloading it because of the spark knock). At any rate, I noticed the 09 doing what you're talking about. If you slowed down fairly quick, you could feel the last two downshifts in the transmission. It felt more like a bump than a push on this one, truck had 60k or so miles. I mentioned it to the dealer and he said it was probably normal. I told him it might be common, as in it happens a lot, but I was pretty sure it wasn't normal, as in its supposed to do that. At any rate, I didn't trade for that one. I wish you luck. Two seperate dealerships have told me the spark knock is normal on my truck also. I think I want my 94 Z71 back lol.

  7. #17

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    I experienced some of the same issues you seem to be having with your Silverado. I own a 2011 Silverado Texas Edition and when coming to a stop the truck would lunge forward as it downshifts. The only way I was able to get rid of it was a custom tune from Blackbear Performance. After speaking a little bit with Justin he said that was a common issue that others have also experienced. I now have MUCH smoother downshifts (don't even notice them) and the truck now performs as it should have from the dealership. I now have my AFM disabled unless I am going over 60 MPH.

  8. #18

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    I'm grasping at straws here... But how does the engine run? Im wondering if a faulty throttle position sensor or something could be causing it... Like what others are saying a high rpm at idle... Or the truck is not returning to idle properly. Maybe you could have the reflash the ecm and tcm? This would not take much on their part. Good luck.
    2009 Chevy Silverado 2500HDLT 6.0L w/ Towing Package, Dick Cepek GM8 Rims, Dick Cepek FC II 33X11.50R17,RKSport Ram-Air Hood(Functional), Lazer Lite Aluminum Tonneau Cover, Road Armor Stealth Bumper, PIAA Lighting, Diablo Trinity Tuner, Diablew Custom Tune, BullyDog Cold Air Intake, American Racing Headers w/highflow cats, Corsa Performance Sport Exhaust, Custom Striping, Black Bowties front and rear, Fuel Grille Inserts, Recon Headlights, Readylift Shocks, Readylift Upper Contol Arms, 2" Blocks in the Rear..

    Future Plans: HD Tie Rods, Under hood upgrades, Crower Camshaft and possibly electric fans.

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