2011 Sierra 5.3 6spd - shudder/heavy vibration under light accel after coasting

Knowles Richard

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Hello Double D & truckers I have a 2013 gmc sierra sle 5.3 SL80 transmission by putting the trans in (M) mode on shifter And then pressing the toggle switch to 5th gear This disables the AFM or v8/v4 so that its all the time v8 My truck also stays in all time v8 when in tow haul mode But its not good city driving RPMs to high on up shifts Eats Gas I got a diablo P2 and deleted that Stinking AFM. Weird exhaust noise GONE vibration GONE.Much Better performance I am happy that's how it worked for my truck hope this helps
 

GregNH

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I have a 2011 Denali 6.2 that does not have AFM but I have the shudder when trying to slightly press gas at highway speeds mostly. I have seen this Service Bulletin but again it states AFM and I don't have that. https://static.nhtsa.gov/odi/tsbs/2015/MC-10113542-9999.pdf

Seems like GM is having people PM them but no solution is being posted. The part in the SB does not fit my tranny anyway according to one site.
 

Julie Acosta

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I have a 2011 Tahoe 1500 5.3 4wd. I've never, ever used the 4wd. 117k miles- I too am having this issue. Coasting at about 30mph when the vibrations comes on and goes out 1-2 seconds. I've just picked it up from the dealer where they ran the diagnostics, changed a few hoses, replaced transmission fluid, serviced Stabilitrak,... rattle/vibration is still there. My previous Tahoe had the transmission go out at 114k so I thought this rattling was an indication the same thing was happening. Transmission checked fine. Anyone have an update to how to fix this? I know nothing of cars so any detailed explanation would help if I can get it to dealer to re-check.
 
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